Getting the mean value for every Id in a data frame

Question

Imagine I have a data frame with 2 columns

Id    Value
12    13
32    3
6022  11
9142  231
12    23
119   312
...

and I want to get the mean value for each "Id". Do you know of any fast way of doing this?

Possible duplicate of [How to average columns based on ID in R?](https://stackoverflow.com/questions/32487367/how-to-average-columns-based-on-id-in-r) — M--, Jul 25 '17 at 21:29

score 8 · Answer 1 · answered Sep 26 '10 at 08:54

8

One possible solution using aggregate:

aggregate(Value ~ Id, data=tmp, FUN=mean)

answered Sep 26 '10 at 08:54

rcs

score 3 · Answer 2 · answered Sep 27 '10 at 10:17

3

Just for completeness basic solution is tapply:

tapply(data$Value, data$Id, mean)

(or using with as with(data, tapply(Value, Id, mean)))

answered Sep 27 '10 at 10:17

Marek

score 2 · Answer 3 · answered Sep 27 '10 at 04:08

2

I heart reshape:

cast(x, Id ~ ., mean)

answered Sep 27 '10 at 04:08

Brandon Bertelsen

score 1 · Accepted Answer · answered Sep 26 '10 at 08:57

1

Beyond aggregate, other options include by and ddply (in plyr).

answered Sep 26 '10 at 08:57

Shane

3

I think you know that this would be considered as a low quality answer. I'd appreciate if you would edit and include some codes. Cheers. – M-- Jul 25 '17 at 21:28

score 0 · Answer 5 · answered Sep 26 '10 at 09:49

0

Also by will do the job, yet the output will be tricky.

answered Sep 26 '10 at 09:49

mbq

5 Answers5