CODEWITHSUNDEEP
rdplyrsample
giac
giac

Reputation: 4299

Sample by groupy with a condition (r)

I need to randomly select a diary for each individual (id) but only for those who filled more than one.

Let us suppose my data look like this 

dta = rbind(c(1, 1, 'a'), 
      c(1, 2, 'a'), 
      c(1, 3, 'b'), 
      c(2, 1, 'a'), 
      c(3, 1, 'b'), 
      c(3, 2, 'a'), 
      c(3, 3, 'c'))

colnames(dta) <- c('id', 'DiaryNumber', 'type')
dta = as.data.frame(dta)
dta

  id     DiaryNumber type
  1             1    a
  1             2    a
  1             3    b
  2             1    a
  3             1    b
  3             2    a
  3             3    c

For example, id 1 filled 3 diaries. What I need is to randomly select one of the 3 diaries. Id 2 only filled one diary, so I do not need to do anything with it.

I have no idea how I could do that. Any ideas ?

Upvotes: 1

Views: 1192

Answers (2)

mpalanco
mpalanco

Reputation: 13570

Base package:

set.seed(123)
df <- lapply(split(dta, dta$id), function(x) x[sample(nrow(x), 1), ])
do.call("rbind", df)

Output:

  id DiaryNumber type
1  1           1    a
2  2           1    a
3  3           2    a

Upvotes: 1

A5C1D2H2I1M1N2O1R2T1
A5C1D2H2I1M1N2O1R2T1

Reputation: 193517

You can use sample_n:

library(dplyr)
dta %>% group_by(id) %>% sample_n(1)
## Source: local data frame [3 x 3]
## Groups: id
## 
##   id DiaryNumber type
## 1  1           2    a
## 2  2           1    a
## 3  3           1    b

Upvotes: 4

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