: how to select rows at random

Hi dear list,

I have a list of around 2000 identifiers aranged in a dataframe in one
column and I would like to choose a random subset of these. I wonder
if somebody can tell me if I could do this with R...

Not sure what you mean by identifiers, but to select a subset of the
2000 cells in that column, you could use sample(). See ?sample for
details, but here is an example.

## choose a random subset of 500 out of 2000 entries
## dummy data
dat <- data.frame(identifiers = sample(2000, 2000), X = rnorm(2000))
## set seed to make this the same on your PC as mine
## comment this if you want a different subset each time you run
set.seed(1234)
## random subset of 500
want <- sample(2000, 500)
## select out that subset
## head to show only first n of the selected
head(dat$identifiers[want])

Gives:

head(dat$identifiers[want])

[1] 1327  587  835  430 1422 1687

This assumes the identifiers are unique.

HTH

G

Thank you so much!

Laura RM

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