Sample random rows in dataframe

First make some data:

> df = data.frame(matrix(rnorm(20), nrow=10))> df           X1         X21   0.7091409 -1.40613612  -1.1334614 -0.19738463   2.3343391 -0.43850714  -0.9040278 -0.65936775   0.4180331 -1.25924156   0.7572246 -0.54636557  -0.8996483  0.42311178  -1.0356774 -0.16408839  -0.3983045  0.715750610 -0.9060305  2.3234110

Then select some rows at random:

> df[sample(nrow(df), 3), ]           X1         X29  -0.3983045  0.71575062  -1.1334614 -0.197384610 -0.9060305  2.3234110

The answer John Colby gives is the right answer. However if you are a dplyr user there is also the answer sample_n:

sample_n(df, 10)

randomly samples 10 rows from the dataframe. It calls sample.int, so really is the same answer with less typing (and simplifies use in the context of magrittr since the dataframe is the first argument).

The data.table package provides the function DT[sample(.N, M)], sampling M random rows from the data table DT.

library(data.table)set.seed(10)mtcars <- data.table(mtcars)mtcars[sample(.N, 6)]    mpg cyl  disp  hp drat    wt  qsec vs am gear carb1: 14.7   8 440.0 230 3.23 5.345 17.42  0  0    3    42: 19.2   6 167.6 123 3.92 3.440 18.30  1  0    4    43: 17.3   8 275.8 180 3.07 3.730 17.60  0  0    3    34: 21.5   4 120.1  97 3.70 2.465 20.01  1  0    3    15: 22.8   4 108.0  93 3.85 2.320 18.61  1  1    4    16: 15.5   8 318.0 150 2.76 3.520 16.87  0  0    3    2