[R] dataframe indexing by number of cases per group

[Dennis Murphy]

A very similar question was asked a couple of days ago - see the
thread titled "Removing rows in dataframe w'o duplicated values" - in
particular, the responses by Dimitris Rizopoulos and David Winsemius.
The adaptation to this problem is

df[ave(as.numeric(df$group), as.numeric(df$group), FUN = length) > 4, ]
   group        x
1      A 3.903747
2      A 3.599547
3      A 2.449991
4      A 2.740639
5      A 4.268988
6      B 8.649600
7      B 5.493841
8      B 1.892154
9      B 6.781754
10     B 1.459250
11     B 6.749522

HTH,
Dennis

On Thu, Nov 24, 2011 at 4:02 AM, Johannes Radinger <JRadinger at gmx.at> wrote:
> Hello,
>
> assume we have following dataframe:
>
> group <-c(rep("A",5),rep("B",6),rep("C",4))
> x <- c(runif(5,1,5),runif(6,1,10),runif(4,2,15))
> df <- data.frame(group,x)
>
> Now I want to select all cases (rows) for those groups
> which have more or equal 5 cases (so I want to select
> all cases of group A and B).
> How can I use the indexing for such questions?
>
> df[??]... I think it is probably quite easy but I really
> don't know how to do that at the moment.
>
> maybe someone can help me...
>
> /johannes
> --
>
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