String functions

Learn how to use and combine different string functions in APL

String functions

Function Name	Description
base64_encode_tostring()	Encodes a string as base64 string.
base64_decode_tostring()	Decodes a base64 string to a UTF-8 string.
countof()	Counts occurrences of a substring in a string.
countof_regex()	Counts occurrences of a substring in a string. Regex matches don’t.
coalesce()	Evaluates a list of expressions and returns the first non-null (or non-empty for string) expression.
extract()	Get a match for a regular expression from a text string.
extract_all()	Get all matches for a regular expression from a text string.
format_bytes()	Formats a number of bytes as a string including bytes units
format_url()	Formats an input string into a valid URL by adding the necessary protocol if it’s escaping illegal URL characters.
indexof()	Function reports the zero-based index of the first occurrence of a specified string within input string.
isempty()	Returns true if the argument is an empty string or is null.
isnotempty()	Returns true if the argument isn’t an empty string or a null.
isnotnull()	Returns true if the argument is not null.
isnull()	Evaluates its sole argument and returns a bool value indicating if the argument evaluates to a null value.
parse_bytes()	Parses a string including byte size units and returns the number of bytes
parse_json()	Interprets a string as a JSON value) and returns the value as dynamic.
parse_url()	Parses an absolute URL string and returns a dynamic object contains all parts of the URL.
parse_urlquery()	Parses a url query string and returns a dynamic object contains the Query parameters.
replace()	Replace all regex matches with another string.
replace_regex()	Replaces all regex matches with another string.
replace_string()	Replaces all string matches with another string.
reverse()	Function makes reverse of input string.
split()	Splits a given string according to a given delimiter and returns a string array with the contained substrings.
strcat()	Concatenates between 1 and 64 arguments.
strcat_delim()	Concatenates between 2 and 64 arguments, with delimiter, provided as first argument.
strcmp()	Compares two strings.
strlen()	Returns the length, in characters, of the input string.
strrep()	Repeats given string provided number of times (default = 1).
substring()	Extracts a substring from a source string starting from some index to the end of the string.
toupper()	Converts a string to upper case.
tolower()	Converts a string to lower case.
trim()	Removes all leading and trailing matches of the specified cutset.
trim_regex()	Removes all leading and trailing matches of the specified regular expression.
trim_end()	Removes trailing match of the specified cutset.
trim_end_regex()	Removes trailing match of the specified regular expression.
trim_start()	Removes leading match of the specified cutset.
trim_start_regex()	Removes leading match of the specified regular expression.
url_decode()	The function converts encoded URL into a regular URL representation.
url_encode()	The function converts characters of the input URL into a format that can be transmitted over the Internet.
gettype()	Returns the runtime type of its single argument.
parse_csv()	Splits a given string representing a single record of comma-separated values and returns a string array with these values.

Each argument has a required section which is denoted with required or optional

• If it’s denoted by required it means the argument must be passed into that function before it’ll work.
• if it’s denoted by optional it means the function can work without passing the argument value.

base64_encode_tostring()

Encodes a string as base64 string.

Arguments

Name	Type	Required or Optional	Description
String	string	Required	Input string or string field to be encoded as base64 string.

Returns

Returns the string encoded as base64 string.

• To decode base64 strings to UTF-8 strings, see base64_decode_tostring()

Examples

base64_encode_tostring(string)

['sample-http-logs']
| project encoded_base64_string = base64_encode_tostring(content_type)

Run in Playground

base64_decode_tostring()

Decodes a base64 string to a UTF-8 string.

Arguments

Name	Type	Required or Optional	Description
String	string	Required	Input string or string field to be decoded from base64 to UTF8-8 string.

Returns

Returns UTF-8 string decoded from base64 string.

• To encode strings to base64 string, see base64_encode_tostring()

Examples

base64_decode_tostring(string)

['sample-http-logs']
| project decoded_base64_string = base64_decode_tostring("VGhpcyBpcyBhbiBlbmNvZGVkIG1lc3NhZ2Uu")

Run in Playground

countof()

Counts occurrences of a substring in a string.

Arguments

name	type	description	Required or Optional
text source	string	Source to count your occurences from	Required
search	string	The plain string to match inside source.	Required

Returns

The number of times that the search string can be matched.

Examples

countof(search, text)

['sample-http-logs']
| project count = countof("con", "content_type")

Run in Playground

countof_regex()

Counts occurrences of a substring in a string. regex matches don’t.

Arguments

• text source: A string.
• regex search: regular expression to match inside your text source.

Returns

The number of times that the search string can be matched in the dataset. Regex matches do not.

Examples

countof_regex(regex, text)

['sample-http-logs']
| project count = countof_regex("c.n", "content_type")

Run in Playground

coalesce()

Evaluates a list of expressions and returns the first non-null (or non-empty for string) expression.

Arguments

name	type	description	Required or Optional
arguments	scalar	The expression or field to be evaluated.	Required

Returns

The value of the first argument whose value isn’t null (or not-empty for string expressions).

Examples

['sample-http-logs']
| project coalesced = coalesce(content_type, ['geo.city'], method)

Run in Playground

['http-logs']
| project req_duration_ms, server_datacenter, predicate = coalesce(content_type, method, status)

Run in Playground

extract()

Retrieve the first substring matching a regular expression from a source string.

Arguments

name	type	description
regex	expression	A regular expression.
captureGroup	int	A positive int constant indicating the capture group to extract. 0 stands for the entire match, 1 for the value matched by the first ’(‘parenthesis’)’ in the regular expression, 2 or more for subsequent parentheses.
source	string	A string to search

Returns

If regex finds a match in source: the substring matched against the indicated capture group captureGroup, optionally converted to typeLiteral.

If there’s no match, or the type conversion fails: -1 or string error

Examples

extract(regex, captureGroup, source)

['sample-http-logs']
| project extract_sub =  extract("^.{2,2}(.{4,4})", 1, content_type)

Run in Playground

extract("x=([0-9.]+)", 1, "axiom x=65.6|po") == "65.6"

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extract_all()

Retrieve all substrings matching a regular expression from a source string. Optionally, retrieve only a subset of the matching groups.

Arguments

name	type	description	Required or Optional
regex	expression	A regular expression containing between one and 16 capture groups. Examples of a valid regex: @”(\d+)”. Examples of an invalid regex: @“\d+“	Required
captureGroups	array	A dynamic array constant that indicates the capture group to extract. Valid values are from 1 to the number of capturing groups in the regular expression.	optional
source	string	A string to search	Required

Returns

• If regex finds a match in source: Returns dynamic array including all matches against the indicated capture groups captureGroups, or all of capturing groups in the regex.
• If number of captureGroups is 1: The returned array has a single dimension of matched values.
• If number of captureGroups is more than 1: The returned array is a two-dimensional collection of multi-value matches per captureGroups selection, or all capture groups present in the regex if captureGroups is omitted.
• If there’s no match: -1

Examples

extract_all(regex, [captureGroups,] source)

['sample-http-logs']
| project extract_match =  extract_all(@"(\w)(\w+)(\w)", dynamic([1,3]), content_type)

Run in Playground

extract_all(@"(\w)(\w+)(\w)", dynamic([1,3]), content_type) == [["t", "t"],["c","v"]]

format_bytes()

Formats a number as a string representing data size in bytes.

Arguments

name	type	description	Required or Optional
value	number	a number to be formatted as data size in bytes	Required
precision	number	Number of digits the value will be rounded to. (default value is zero)	Optional
units	string	Units of the target data size the string formatting will use (base 2 suffixes: Bytes, KiB, KB, MiB, MB, GiB, GB, TiB, TB, PiB, EiB, ZiB, YiB; base 10 suffixes: kB MB GB TB PB EB ZB YB). If the parameter is empty the units will be auto-selected based on input value.	Optional
base	number	Either 2 or 10 to specify whether the prefix is calculated using 1000s or 1024s for each type. (default value is 2)	Optional

Returns

• A formatted string for humans

Examples

format_bytes( 4000, number, "['id']", num_comments ) == "3.9062500000000 KB"

format_bytes(value [, precision [, units [, base]]])

format_bytes(1024) == "1 KB"

format_bytes(8000000, 2, "MB", 10) == "8.00 MB"

['github-issues-event']
| project formated_bytes =  format_bytes( 4783549035, number, "['id']", num_comments  )

Run in Playground

format_url()

Formats an input string into a valid URL. This function will return a string that is a properly formatted URL.

Arguments

name	type	description	Required or Optional
url	dynamic	string input you want to format into a URL	Required

Returns

• A string that represents a properly formatted URL.

Examples

['sample-http-logs']
| project formatted_url = format_url(dynamic({"scheme": "https", "host": "github.com", "path": "/axiomhq/next-axiom"})

Run in Playground

['sample-http-logs']
| project formatted_url = format_url(dynamic({"scheme": "https", "host": "github.com", "path": "/axiomhq/next-axiom", "port": 443, "fragment": "axiom","user": "axiom", "password": "apl"}))

Run in Playground

• These are all the supported keys when using the format_url function: scheme, host, port, fragment, user, password, query.

indexof()

Reports the zero-based index of the first occurrence of a specified string within the input string.

Arguments

name	type	description	usage
source	string	Input string	Required
lookup	string	String to look up	Required
start_index	text	Search start position.	Optional
length	characters	Number of character positions to examine. A value of -1 means unlimited length.	Optional
occurrence	number	The number of the occurrence. Default 1.	Optional

Returns

• Zero-based index position of lookup.

• Returns -1 if the string isn’t found in the input.

Examples

indexof( body, ['id'], 2, 1, number ) == "-1"

indexof(source,lookup[,start_index[,length[,occurrence]]])

indexof ()

['github-issues-event']
| project occurrence = indexof( body, ['id'], 23, 5, number )

Run in Playground

isempty()

Returns true if the argument is an empty string or is null.

Returns

Indicates whether the argument is an empty string or isnull.

Examples

isempty("") == true

isempty([value])

['github-issues-event']
| project empty = isempty(num_comments)

Run in Playground

isnotempty()

Returns true if the argument isn’t an empty string, and it isn’t null.

Examples

isnotempty("") == false

isnotempty([value])

notempty([value]) -- alias of isnotempty

['github-issues-event']
| project not_empty = isnotempty(num_comments)

Run in Playground

isnotnull()

Returns true if the argument is not null.

Examples

isnotnull( num_comments ) == true

isnotnull([value])

notnull([value]) - alias for `isnotnull`

['github-issues-event']
| project not_null = isnotnull(num_comments)

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isnull()

Evaluates its sole argument and returns a bool value indicating if the argument evaluates to a null value.

Returns

True or false, depending on whether or not the value is null.

Examples

isnull(Expr)

['github-issues-event']
| project is_null = isnull(creator)

Run in Playground

parse_bytes()

Parses a string including byte size units and returns the number of bytes

Arguments

name	type	description	Required or Optional
bytes_string	string	A string formated defining the number of bytes	Required
base	number	(optional) Either 2 or 10 to specify whether the prefix is calculated using 1000s or 1024s for each type. (default value is 2)	Required

Returns

• The number of bytes or zero if unable to parse

Examples

parse_bytes(bytes_string [, base])

parse_bytes("1 KB") == 1024

parse_bytes("1 KB", 10) == 1000

parse_bytes("128 Bytes") == 128

parse_bytes("bad data") == 0

['github-issues-event']
| extend parsed_bytes =  parse_bytes("300 KB", 10)

Run in Playground

['github-issues-event']
| project parsed_bytes =  parse_bytes("300 KB", 10)

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parse_json()

Interprets a string as a JSON value and returns the value as dynamic.

Arguments

Name	Type	Required or Optional	Description
Json Expr	string	Required	Expression that will be used, also represents a JSON-formatted value

Returns

An object of type json that is determined by the value of json:

• If json is of type string, and is a properly formatted JSON string, then the string is parsed, and the value produced is returned.

• If json is of type string, but it isn’t a properly formatted JSON string, then the returned value is an object of type dynamic that holds the original string value.

Examples

parse_json(json)

['vercel']
| extend parsed = parse_json('{"name":"vercel", "statuscode":200, "region": { "route": "usage streams", "number": 9 }}')

['github-issues-event']
| extend parsed = parse_json(creator)
| where isnotnull( parsed)

Run in Playground

parse_url()

Parses an absolute URL string and returns an object contains URL parts.

Arguments

Name	Type	Required or Optional	Description
URL	string	Required	A string represents a URL or the query part of the URL.

Returns

An object of type dynamic that included the URL components: Scheme, Host, Port, Path, Username, Password, Query Parameters, Fragment.

Examples

parse_url(url)

['sample-http-logs']
| extend ParsedURL = parse_url("https://www.example.com/path/to/page?query=example")
| project 
  Scheme = ParsedURL["scheme"],
  Host = ParsedURL["host"],
  Path = ParsedURL["path"],
  Query = ParsedURL["query"]

Run in Playground

• Result

{
  "Host": "www.example.com",
  "Path": "/path/to/page",
  "Query": {
    "query": "example"
  },
  "Scheme": "https"
}

parse_urlquery()

Returns a dynamic object contains the Query parameters.

Arguments

Name	Type	Required or Optional	Description
Query	string	Required	A string represents a url query.

query: A string represents a url query

Returns

An object of type dynamic that includes the query parameters.

Examples

parse_urlquery("a1=b1&a2=b2&a3=b3")

Run in Playground

• Result

{
  "Result": {
    "a3": "b3",
    "a2": "b2",
    "a1": "b1"
  }
}

parse_urlquery(query)

['github-issues-event']
| project parsed = parse_urlquery("https://play.axiom.co/axiom-play-qf1k/query?qid=fUKgiQgLjKE-rd7wjy")

Run in Playground

replace()

Replace all regex matches with another string.

Arguments

• regex: The regular expression to search source. It can contain capture groups in ’(‘parentheses’)’.
• rewrite: The replacement regex for any match made by matchingRegex. Use $0 to refer to the whole match,$1 for the first capture group, $2 and so on for subsequent capture groups.
• source: A string.

Returns

• source after replacing all matches of regex with evaluations of rewrite. Matches do not overlap.

Examples

replace(regex, rewrite, source)

['sample-http-logs']
| project content_type, Comment = replace("[html]", "[censored]", method)

Run in Playground

replace_regex()

Replaces all regex matches with another string.

Arguments

• regex: The regular expression to search text.
• rewrite: The replacement regex for any match made by matchingRegex.
• text: A string.

Returns

source after replacing all matches of regex with evaluations of rewrite. Matches do not overlap.

Examples

replace_regex(@'^logging', 'axiom', 'logging-data')

• Result

{
  "replaced": "axiom-data"
}

replace_regex(regex, rewrite, text)

['github-issues-event']
| extend replaced = replace_regex(@'^logging', 'axiom', 'logging-data')

Run in Playground

Backreferences

Backreferences match the same text as previously matched by a capturing group. With Backreferences, you can identify a repeated character or substring within a string.

• Backreferences in APL is implemented using the $ sign.

Examples

['github-issues-event']
| project backreferences = replace_regex(@'observability=(.+)', 'axiom=$1', creator)

Run in Playground

replace_string()

Replaces all string matches with another string.

Arguments

Name	Type	Required or Optional	Description
lookup	string	Required	A string which Axiom matches in text and replaces with rewrite.
rewrite	string	Required	A string with which Axiom replaces parts of text that match lookup.
text	string	Required	A string where Axiom replaces parts matching lookup with rewrite.

Returns

text after replacing all matches of lookup with evaluations of rewrite. Matches don’t overlap.

Examples

replace_string("github", "axiom", "The project is hosted on github")

• Result

{
  "replaced_string": "axiom"
}

replace_string(lookup, rewrite, text)

['sample-http-logs']
| extend replaced_string = replace_string("The project is hosted on github", "github", "axiom")
| project replaced_string

Run in Playground

reverse()

Function reverses the order of the input Field.

Arguments

name	type	description	Required or Optional
Field	string	Field input value	Required

Returns

The reverse order of a field value.

Examples

reverse(value)

project reversed = reverse("axiom")

Run in Playground

• Result

moixa

split()

Splits a given string according to a given delimiter and returns a string array with the contained substrings.

Optionally, a specific substring can be returned if exists.

Arguments

• source: The source string that will be split according to the given delimiter.
• delimiter: The delimiter (Field) that will be used in order to split the source string.

Returns

• A string array that contains the substrings of the given source string that are delimited by the given delimiter.

Examples

split(source, delimiter)

project split_str = split("axiom_observability_monitoring", "_")

Run in Playground

• Result

{
  "split_str": ["axiom", "observability", "monitoring"]
}

strcat()

Concatenates between 1 and 64 arguments.

If the arguments aren’t of string type, they’ll be forcibly converted to string.

Arguments

Name	Type	Required or Optional	Description
Expr	string	Required	Expressions to be concatenated.

Returns

Arguments, concatenated to a single string.

Examples

strcat(argument1, argument2[, argumentN])

['github-issues-event']
| project stract_con = strcat( ['milestone.creator'], number )

Run in Playground

['github-issues-event']
| project stract_con = strcat( 'axiom', number )

Run in Playground

• Result

{
  "stract_con": "axiom3249"
}

strcat_delim()

Concatenates between 2 and 64 arguments, with delimiter, provided as first argument.

• If arguments aren’t of string type, they’ll be forcibly converted to string.

Arguments

Name	Type	Required or Optional	Description
delimiter	string	Required	string expression, which will be used as separator.
argument1 ..	string	Required	Expressions to be concatenated.

Returns

Arguments, concatenated to a single string with delimiter.

Examples

strcat_delim(delimiter, argument1, argument2[ , argumentN])

['github-issues-event']
| project strcat = strcat_delim(":", actor, creator)

Run in Playground

project strcat = strcat_delim(":", "axiom", "monitoring")

• Result

{
  "strcat": "axiom:monitoring"
}

strcmp()

Compares two strings.

The function starts comparing the first character of each string. If they are equal to each other, it continues with the following pairs until the characters differ or until the end of shorter string is reached.

Arguments

Name	Type	Required or Optional	Description
string1	string	Required	first input string for comparison.
string2	string	Required	second input string for comparison.

Returns

Returns an integral value indicating the relationship between the strings:

• When the result is 0: The contents of both strings are equal.
• When the result is -1: the first character that does not match has a lower value in string1 than in string2.
• When the result is 1: the first character that does not match has a higher value in string1 than in string2.

Examples

strcmp(string1, string2)

['github-issues-event']
| extend cmp = strcmp( body, repo )

Run in Playground

project cmp = strcmp( "axiom", "observability")

• Result

{
  "input_string": -1
}

strlen()

Returns the length, in characters, of the input string.

Arguments

Name	Type	Required or Optional	Description
source	string	Required	The source string that will be measured for string length.

Returns

Returns the length, in characters, of the input string.

Examples

strlen(source)

project str_len =  strlen("axiom")

Run in Playground

• Result

{
  "str_len": 5
}

strrep()

Repeats given string provided amount of times.

• In case if first or third argument is not of a string type, it will be forcibly converted to string.

Arguments

Name	Type	Required or Optional	Description
value	Expr	Required	Inpute Expression
multiplier	integer	Required	positive integer value (from 1 to 1024)
delimiter	string	Optional	An optional string expression (default: empty string)

Returns

• Value repeated for a specified number of times, concatenated with delimiter.

• In case if multiplier is more than maximal allowed value (1024), input string will be repeated 1024 times.

Examples

strrep(value,multiplier,[delimiter])

['github-issues-event']
| extend repeat_string = strrep( repo, 5, "::" )

Run in Playground

project repeat_string = strrep( "axiom", 3, "::" )

• Result

{
  "repeat_string": "axiom::axiom::axiom"
}

substring()

Extracts a substring from a source string starting from some index to the end of the string.

Arguments

• source: The source string that the substring will be taken from.
• startingIndex: The zero-based starting character position of the requested substring.
• length: A parameter that can be used to specify the requested number of characters in the substring.

Returns

A substring from the given string. The substring starts at startingIndex (zero-based) character position and continues to the end of the string or length characters if specified.

Examples

substring(source, startingIndex [, length])

['github-issues-event']
| extend extract_string = substring( repo, 4, 5 )

Run in Playground

project extract_string = substring( "axiom", 4, 5 )

{
  "extract_string": "m"
}

toupper()

Converts a string to upper case.

toupper("axiom") == "AXIOM"

['github-issues-event']
| project upper = toupper( body )

Run in Playground

tolower()

Converts a string to lower case.

tolower("AXIOM") == "axiom"

['github-issues-event']
| project low = tolower( body )

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trim()

Removes all leading and trailing matches of the specified cutset.

Arguments

• source: A string.
• cutset: A string containing the characters to be removed.

Returns

source after trimming matches of the cutset found in the beginning and/or the end of source.

Examples

trim(source)

['github-issues-event']
| extend remove_leading_matches = trim( "locked", repo)

Run in Playground

project remove_leading_matches = trim( "axiom", "observability")

• Result

{
  "remove_leading_matches": "bservability"
}

trim_regex()

Removes all leading and trailing matches of the specified regular expression.

Arguments

• regex: String or regular expression to be trimmed from the beginning and/or the end of source.
• source: A string.

Returns

source after trimming matches of regex found in the beginning and/or the end of source.

Examples

trim_regex(regex, source)

['github-issues-event']
| extend remove_trailing_match_regex = trim_regex( "^github", action )

Run in Playground

• Result

{
  "remove_trailing_match_regex": "closed"
}

trim_end()

Removes trailing match of the specified cutset.

Arguments

• source: A string.
• cutset: A string containing the characters to be removed.`

Returns

source after trimming matches of the cutset found in the end of source.

Examples

trim_end(source)

['github-issues-event']
| extend remove_cutset = trim_end(@"[^\w]+", body)

Run in Playground

• Result

{
  "remove_cutset": "In [`9128d50`](https://7aa98788e07\n), **down**:\n- HTTP code: 0\n- Response time: 0 ms\n"
}

trim_end_regex()

Removes trailing match of the specified regular expression.

Arguments

• regex: String or regular expression to be trimmed from the end of source.
• source: A string.

Returns

source after trimming matches of regex found in the end of source.

Examples

trim_end_regex(regex, source)

['github-issues-event']
| project remove_cutset_regex = trim_end_regex( "^github", creator )

Run in Playground

• Result

{
  "remove_cutset_regex": "axiomhq"
}

trim_start()

Removes leading match of the specified cutset.

Arguments

• source: A string.

Returns

• source after trimming match of the specified cutset found in the beginning of source.

Examples

trim_start(source)

['github-issues-event']
| project remove_cutset = trim_start( "github", repo)

Run in Playground

• Result

{
  "remove_cutset": "axiomhq/next-axiom"
}

trim_start_regex()

Removes leading match of the specified regular expression.

Arguments

• regex: String or regular expression to be trimmed from the beginning of source.
• source: A string.

Returns

source after trimming match of regex found in the beginning of source.

Examples

trim_start_regex(regex, source)

['github-issues-event']
| project remove_cutset = trim_start_regex( "github", repo)

Run in Playground

• Result

{
  "remove_cutset": "axiomhq/next-axiom"
}

url_decode()

The function converts encoded URL into a to regular URL representation.

Arguments

• encoded url: encoded URL (string).

Returns

URL (string) in a regular representation.

Examples

url_decode(encoded url)

['github-issues-event']
| project decoded_link = url_decode( "https://www.axiom.co/" )

Run in Playground

• Result

{
  "decoded_link": "https://www.axiom.co/"
}

url_encode()

The function converts characters of the input URL into a format that can be transmitted over the Internet.

Arguments

• url: input URL (string).

Returns

URL (string) converted into a format that can be transmitted over the Internet.

Examples

url_encode(url)

['github-issues-event']
| project encoded_url = url_encode( "https://www.axiom.co/" )

Run in Playground

• Result

{
  "encoded_link": "https%3A%2F%2Fwww.axiom.co%2F"
}

gettype()

Returns the runtime type of its single argument.

Arguments

• Expressions

Returns

A string representing the runtime type of its single argument.

Examples

Expression	Returns
gettype(“lima”)	string
gettype(2222)	int
gettype(5==5)	bool
gettype(now())	datetime
gettype(parse_json(‘67’))	int
gettype(parse_json(’ “polish” ‘))	string
gettype(parse_json(’ {“axiom”:1234} ‘))	dictionary
gettype(parse_json(’ [6, 7, 8] ‘))	array
gettype(456.98)	real
gettype(parse_json(”))	null

parse_csv()

Splits a given string representing a single record of comma-separated values and returns a string array with these values.

Arguments

• csv_text: A string representing a single record of comma-separated values.

Returns

A string array that contains the split values.

Examples

parse_csv("axiom,logging,observability") ==  [ "axiom", "logging", "observability" ]

parse_csv("axiom, processing, language")  == [ "axiom", "processing", "language" ]

['github-issues-event']
| project parse_csv("github, body, repo")

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