[R] vector indexing problem in multilevel data: assigning a specific value to all group members

[Gabor Grothendieck]

Try this. The function f takes a vector of indices and returns the
attribute for the unique groupLeader row among them.  We use ave to
apply to each set of indices having a common groupId.

f <- function(ix) with(df[ix,], someAttribute[groupLeader == 1])
transform(df, leaderAttribute = ave(1:nrow(df), df$groupId, FUN = f))



On Tue, Dec 22, 2009 at 5:42 AM, Bertolt Meyer <bmeyer at sozpsy.uzh.ch> wrote:
> Dear List,
>
> I work with multilevel data from psychological group experiments and have
> frequently encountered a situation for which I haven't found an elegant
> solution: I need to assign the value of a specific group member to all
> members of the group. For example, I have a group leader (identified by a
> binary vector) and some attribute for all group members. I want to create a
> new vector that holds the attribute of the group leader for each individual
> in the data frame (code at the bottom of the post):
>
>  personId groupId groupLeader someAttribute leaderAttribute
> 1        1      17           0   0.145833333              NA
> 2        2      17           1   0.218750000              NA
> 3        3      17           0   0.089743590              NA
> 4        4      22           0   0.003875969              NA
> 5        5      22           0   0.086486486              NA
> 6        6      22           0   0.218750000              NA
> 7        7      22           1   0.089743590              NA
> 8        8      37           1   0.016129032              NA
> 9        9      37           0   0.151898734              NA
>
> I need this:
>
>  personId groupId groupLeader someAttribute leaderAttribute
> 1        1      17           0   0.145833333     0.218750000
> 2        2      17           1   0.218750000     0.218750000
> 3        3      17           0   0.089743590     0.218750000
> 4        4      22           0   0.003875969     0.089743590
> 5        5      22           0   0.086486486     0.089743590
> 6        6      22           0   0.218750000     0.089743590
> 7        7      22           1   0.089743590     0.089743590
> 8        8      37           1   0.016129032     0.016129032
> 9        9      37           0   0.151898734     0.016129032
>
> So far, my attemps along the lines of
>
> df$leaderAttribute <- df$someAttribute[df$groupLeader == 1][df$groupId]
>
> have failed if the groups were not numbered with 1, 2, 3... as in the
> example above. I need something simple for transforming the groupId vector
> from 17, 17, 17, 22... to 1,1,1,2... for doing the second indexing. It seems
> like a simple problem, but I am unable to get it right. I had to fall back
> to building a specific function employing nested for() loops for achieving
> this. However, this is error prone and very slow, as some of my data sets
> are very large. What am I missing?
>
> Any help would be greatly appreciated.
> Regards,
> Bertolt
>
> Code:
>
> personId <- c(1,2,3,4,5,6,7,8,9)
> groupId <- c(17,17,17,22,22,22,22,37,37)
> groupLeader <- c(0,1,0,0,0,0,1,1,0)
> someAttribute <- c(0.145833333, 0.218750000, 0.089743590, 0.003875969,
> 0.086486486, 0.218750000, 0.089743590, 0.016129032, 0.151898734)
> leaderAttribute <- c(NA,NA,NA,NA,NA,NA,NA,NA,NA)
>
> df <- cbind(personId, groupId, groupLeader, someAttribute, leaderAttribute)
> df <- as.data.frame(df)
> df
>
> rm(personId, groupId, groupLeader, someAttribute, leaderAttribute, df)
>
> --
> Dr. Bertolt Meyer
> Senior research and teaching associate
> Social Psychology, Institute of Psychology, University of Zurich
> Binzmuehlestrasse 14, Box 15
> CH-8050 Zurich
> Switzerland
>
> bmeyer at sozpsy.uzh.ch
> tel:   +41446357282
> fax:   +41446357279
>
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