Reference · Strings

index_of

index_of(list | str, any) -> int | null

What it does

The position of a value in a list or of a piece of text in a string, counting from 0, or null when it is not there: null, not -1. In a list the first item equal to the value (as == says) counts; in a string the piece is written as text and the first occurrence counts, by characters.

Examples

print(index_of("hello", "l"), index_of("hello", "lo"), index_of("hello", "x"))print(index_of([1, 2, 3, 2], 2), index_of([1, 2, 3], 4))

2 3 null1 null

Edge cases

• Not found is null, so give it ?? -1 where a number is needed, or test for null.
• In a string, case matters, the search is by characters not bytes, and the empty piece is at 0; a number is searched as its text.
• In a list the match is equality: 1 is found in [1.0, 2], "2" is not found in [1, 2]; null, a list or a map inside is found when it is equal.
• The empty string and the empty list hold nothing but "".

print(index_of("hello", "L"), index_of("héllo", "l"), index_of("hello", ""), index_of("a1b", 1))print(index_of([1.0, 2], 1), index_of([1, 2], "2"), index_of([null, 1], null), index_of([[1], [2]], [2]), index_of([{ a: 1 }], { a: 1 }))print(index_of("", ""), index_of("", "a"), index_of([], 1))print(index_of("hello", "x") ?? -1)

null 2 0 10 null 0 1 00 null null-1

Errors

A first argument that is not a list or a string, null included, is a runtime error, not an error value. A map is not searched: use has for its keys.

print(index_of(null, 1))

line 1: `index_of` expects a list or str, got null

Chaining

In a pipeline the list or text comes first and the value is the argument:

print("abc" | index_of("c"), [1, 2] | index_of(2))let i = index_of("key=value", "=")print(slice("key=value", 0, i), slice("key=value", i + 1))print(["a", "b"] | map((s) => index_of("xbx", s)))

2 1key value[null, 1]

See also

contains, slice, find, re.find, has

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