sample {dplyr} | R Documentation

## Sample n rows from a table

### Description

This is a wrapper around `sample.int()` to make it easy to select random rows from a table. It currently only works for local tbls.

### Usage

    sample_n(tbl, size, replace = FALSE, weight = NULL, .env = NULL)

    sample_frac(tbl, size = 1, replace = FALSE, weight = NULL, .env = NULL)

### Arguments

`tbl` | tbl of data.
`size` | For `sample_n()`, the number of rows to select. For `sample_frac()`, the fraction of rows to select. If `tbl` is grouped, `size` applies to each group.
`replace` | Sample with or without replacement?
`weight` | Sampling weights. This must evaluate to a vector of non-negative numbers the same length as the input. Weights are automatically standardised to sum to 1. This argument is automatically quoted and later evaluated in the context of the data frame. It supports unquoting. See `vignette("programming")` for an introduction to these concepts.
`.env` | This variable is deprecated and no longer has any effect. To evaluate `weight` in a particular context, you can now unquote a quosure.

### Examples

    by_cyl <- mtcars %>% group_by(cyl)

    # Sample fixed number per group
    sample_n(mtcars, 10)
    sample_n(mtcars, 50, replace = TRUE)
    sample_n(mtcars, 10, weight = mpg)

    sample_n(by_cyl, 3)
    sample_n(by_cyl, 10, replace = TRUE)
    sample_n(by_cyl, 3, weight = mpg / mean(mpg))

    # Sample fixed fraction per group
    # Default is to sample all data = randomly resample rows
    sample_frac(mtcars)

    sample_frac(mtcars, 0.1)
    sample_frac(mtcars, 1.5, replace = TRUE)
    sample_frac(mtcars, 0.1, weight = 1 / mpg)

    sample_frac(by_cyl, 0.2)
    sample_frac(by_cyl, 1, replace = TRUE)

[Package dplyr version 0.7.0 Index]