# sample

From dplyr v0.3
by Hadley Wickham

##### Sample n rows from a table.

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

##### 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 expression is evaluated in the context of the data frame. It must return a vector of non-negative numbers the same length as the input. Weights are automatically standardised to sum to 1.
- .env
- Environment in which to look for non-data names used in
`weight`

. Non-default settings for experts only.

##### 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)
```

*Documentation reproduced from package dplyr, version 0.3, License: MIT + file LICENSE*

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