﻿ index – Algosim documentation
Algosim documentation: index

# index

Finds the index of a value in an ordered container.

## Syntax

• `index(X, x)`

• `X` is an ordered container

• `x` is any object

• `index(X, x, ε)`

• `X` is an ordered container

• `x` is any object

• `ε` is a non-negative integer

## Description

If `X` is an ordered container and `x` any value, then `index(X, x)` returns the 1-based index of the first occurrence of `x` in `X`. If `x` isn’t present in `X`, `null` is returned.

`index(X, x, ε)` has the same behaviour, but it compares floating-point values with epsilon `ε` if `ε > 0`; if `ε = 0`, a default, non-zero, epsilon is used.

## Examples

`Alice ≔ ExampleData("Alice in Wonderland");`
`index(words(Alice) @ LowerCase, "perfunctorily")`
`index(words(Alice) @ LowerCase, "splendidly")`
`2524`
`A ≔ SequenceVector(10) ⊗ SequenceVector(10)`
```⎛  1    2    3    4    5    6    7    8    9   10⎞
⎜  2    4    6    8   10   12   14   16   18   20⎟
⎜  3    6    9   12   15   18   21   24   27   30⎟
⎜  4    8   12   16   20   24   28   32   36   40⎟
⎜  5   10   15   20   25   30   35   40   45   50⎟
⎜  6   12   18   24   30   36   42   48   54   60⎟
⎜  7   14   21   28   35   42   49   56   63   70⎟
⎜  8   16   24   32   40   48   56   64   72   80⎟
⎜  9   18   27   36   45   54   63   72   81   90⎟
⎝ 10   20   30   40   50   60   70   80   90  100⎠
```
`index(A, 36)`
```9
4
```