Randomizing selection in R
This will give you a sample with 55 record from the larger data-set that you have.

 sample &lt;- df[sample(1:nrow(df), 55, replace=FALSE),]


If you want to make a reproducible example of the sample, you need to set seed like this:

 set.seed(57)
 sample &lt;- df[sample(1:nrow(df), 55, replace=FALSE),]


So later you can use the same seed for getting the same result.

p.s. replace=FALSE means that each record after that has been picked from the df to be included in the sample, will be excluded from the df and it will not be chosen multiple times.