R: Subsetting data.tables

subset.data.table {data.table} | R Documentation

## Subsetting data.tables

### Description

Returns subsets of a `data.table`.

### Usage

      ## S3 method for class 'data.table'
    subset(x, subset, select, ...)

### Arguments

`x` | `data.table` to subset.
`subset` | logical expression indicating elements or rows to keep
`select` | expression indicating columns to select from `data.table`
`...` | further arguments to be passed to or from other methods

### Details

The `subset` argument works on the rows and will be evaluated in the `data.table` so columns can be referred to (by name) as variables in the expression.

The `data.table` that is returned will maintain the original keys as long as they are not `select`-ed out.

### Value

A `data.table` containing the subset of rows and columns that are selected.

### See Also

`subset`

### Examples

    DT <- data.table(a=sample(c('a', 'b', 'c'), 20, replace=TRUE),
                     b=sample(c('a', 'b', 'c'), 20, replace=TRUE),
                     c=sample(20), key=c('a', 'b'))

    sub <- subset(DT, a == 'a')
    all.equal(key(sub), key(DT))

[Package data.table version 1.11.8 Index]