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  4. R: dplyr - Select 'random' rows from a data frame

R: dplyr - Select 'random' rows from a data frame

Mark Needham user avatar by
Mark Needham
·
Dec. 01, 14 · Interview
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Frequently I find myself wanting to take a sample of the rows in a data frame where just taking the head isn’t enough.

Let’s say we start with the following data frame:

data = data.frame(
    letter = sample(LETTERS, 50000, replace = TRUE),
    number = sample (1:10, 50000, replace = TRUE)
    )

And we’d like to sample 10 rows to see what it contains. We’ll start by generating 10 random numbers to represent row numbers using the runif function:

> randomRows = sample(1:length(data[,1]), 10, replace=T)
> randomRows
 [1]  8723 18772  4964 36134 27467 31890 16313 12841 49214 15621

We can then pass that list of row numbers into dplyr’s slice function like so:

> data %>% slice(randomRows)
   letter number
1       Z      4
2       F      1
3       Y      6
4       R      6
5       Y      4
6       V     10
7       R      6
8       D      6
9       J      7
10      E      2

If we’re using that code throughout our code then we might want to pull out a function like so:

pickRandomRows = function(df, numberOfRows = 10) {
  df %>% slice(runif(numberOfRows,0, length(df[,1])))
}

And then call it like so:

> data %>% pickRandomRows()
   letter number
1       W      5
2       Y      3
3       E      6
4       Q      8
5       M      9
6       H      9
7       E     10
8       T      2
9       I      5
10      V      4
 
> data %>% pickRandomRows(7)
  letter number
1      V      7
2      N      4
3      W      1
4      N      8
5      G      7
6      V      1
7      N      7


R (programming language) Row (database) Data (computing) Frame (networking) Dplyr

Published at DZone with permission of Mark Needham, DZone MVB. See the original article here.

Opinions expressed by DZone contributors are their own.

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