Average the value of all the variables groups except one

Question

I have the following data

 id    value

  a       2
  b       3
  c       4
  a       6

I wish to have average of all the data that exclude a group. In other words, I'd like to set the current id apart and take the average of all the others and repeat it for each id. for instance the first one put all a apart and take average of b and c which is 3.5 ( average of 3 and 4) so, I wish to have the following output:

 id    value

  a       3.5
  b       4
  c       3.66

My data

df <- data.frame(id = c("a", "b", "c" , "a"), value = c(2,3,4,6) )

Note that this question is different from averaging each group

@MFR Please use the @ so that I will be notified about your comments. I reopened it. — akrun, Nov 02 '16 at 06:18
The 3.5 value looks correct, but what about the others? i.e. `mean(c(2,4,6)) #[1] 4` — akrun, Nov 02 '16 at 06:25
In that case, `sapply(as.character(unique(df$id)), function(x) mean(subset(df, !id %in% x)$value))` — akrun, Nov 02 '16 at 06:28
Correct @akrun. Thank you. Please consider posting your answer below, then I can accept it — MFR, Nov 02 '16 at 06:30
If you want the previous output i.e. 6, 5.5, then `library(data.table); setDT(df)[, (sum(df$value) - sum(value))/2 , id]` — akrun, Nov 02 '16 at 06:33
No the first solution works perfectly, the first output was a mistake — MFR, Nov 02 '16 at 06:34

akrun · Accepted Answer · 2016-11-02T06:36:26.707

2

One option is data.table

library(data.table)
setDT(df)[,  .(value = (sum(df$value) - sum(value))/(nrow(df)-.N)) , by =  id]
#   id    value
#1:  a 3.500000
#2:  b 4.000000
#3:  c 3.666667

If we need the 6 and 5.5 for 'ids' 'b' and 'c'

 setDT(df)[, .(value = (sum(df$value) - sum(value))/(uniqueN(df$id)-1)) , by = id]
 #   id value
 #1:  a   3.5
 #2:  b   6.0
 #3:  c   5.5

edited Nov 02 '16 at 06:36

answered Nov 02 '16 at 06:34

akrun

874,273
37
540
662

Nicholas Hamilton · Answer 2 · 2016-11-02T07:08:46.103

1

plyr::ddply(df,'id',function(x){ c(value = mean(df[with(df,id != x$id[1]),]$value)) })

edited Nov 02 '16 at 07:08

answered Nov 02 '16 at 07:00

Nicholas Hamilton

10,044
6
57
88

Average the value of all the variables groups except one

2 Answers2