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# Return True Indices of a Logical Object in R Programming – which() Function

• Last Updated : 08 Jun, 2020

`which()` function in R Language is used to return the indices of the object which return true for the logical operation passed as argument.

Syntax: which(x, arr.ind)

Parameters:
x: logical object
arr.ind: Boolean value to display indices

Example 1:

 `# R program to illustrate ``# the use of which() function`` ` `# Create a matrix``x <``-` `matrix(``1``:``9``, ``3``, ``3``)``x`` ` `# Calling which() function``which(x ``%``%` `2` `=``=` `0``, arr.ind ``=` `TRUE)`

Output:

```     [, 1] [, 2] [, 3]
[1, ]    1    4    7
[2, ]    2    5    8
[3, ]    3    6    9
row col
[1, ]   2   1
[2, ]   1   2
[3, ]   3   2
[4, ]   2   3
```

Here, in the above code, the `which()` function returns the indices of all the even numbers present in the matrix.

Example 2:

 `# R program to illustrate ``# the use of which() function`` ` `# Using predefined dataset``BOD`` ` `# Calling which() function``which(BOD\$demand ``=``=` `19``, arr.ind ``=` `TRUE)`

Output:

```  Time demand
1    1    8.3
2    2   10.3
3    3   19.0
4    4   16.0
5    5   15.6
6    7   19.8
 3
```
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