R: Column Indexes

col {base} | R Documentation

## Column Indexes

### Description

Returns a matrix of integers indicating their column number in the matrix.

### Usage

    col(x, as.factor=FALSE)

### Arguments

`x` | a matrix.
`as.factor` | a logical value indicating whether the value should be returned as a factor rather than as numeric.

### Value

An integer matrix with the same dimensions as `x` and whose `ij`-th element is equal to `j`.

### See Also

`row` to get rows.

### Examples

    # extract an off-diagonal of a matrix
    ma <- matrix(1:12, 3, 4)
    ma[row(ma) == col(ma) + 1]

    # create an identity 5-by-5 matrix
    x <- matrix(0, nr = 5, nc = 5)
    x[row(x) == col(x)] <- 1

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