r - Select random row for each unique value in one specific column od fata frame -

i have quite simple request cannot, however, deal use of 1 code line.

all want subset input data frame in way in output data frame there 1 randomly selected row each unique value (factor's level) of 1 particular data frame's column.

e.x. have (v2 particular data frame's column)

   v1 v2 1    1                       2   b  1       3   c  2 4    1 5   b  2 6   b  1 7   b  1 8   c  2 9   d  1 10  e  1 

and want have output data frame:

   v1 v2 1   b  1                       2   c  2   

thank suggestions in advance!

this way more asked for, wrote function called stratified lets take random samples data.frame 1 or more group variables.

you can load , use this:

library(devtools) source_gist("https://gist.github.com/mrdwab/6424112") # [1] "https://raw.github.com/gist/6424112" # sha-1 hash of file 0006d8548785ec8a5651c3dd599648cc88d153a4      ## 1 row stratified(mydf, "v2", 1) #    v1 v2 # 10  e  1 # 8   c  2  ## 2 rows stratified(mydf, "v2", 2) #   v1 v2 # 2  b  1 # 6  b  1 # 3  c  2 # 5  b  2 

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i'll add official documentation function @ point, here's summary best use out of it:

the arguments stratified are:

• df: input data.frame
• group: character vector of column or columns make "strata".
• size: desired sample size.
  • if size value less 1, proportionate sample taken each stratum.
  • if size single integer of 1 or more, number of samples taken each stratum.
  • if size vector of integers, specified number of samples taken each stratum. recommended use named vector. example, if have 2 strata, "a" , "b", , wanted 5 samples "a" , 10 "b", enter size = c(a = 5, b = 10).
• select: allows subset groups in sampling process. list. instance, if group variable "group", , contained 3 strata, "a", "b", , "c", wanted sample "a" , "c", can use select = list(group = c("a", "c")).
• replace: sampling replacement.