number of identical ids in a data frame

Question

I have a data frame with a varying number of group-ids and corresponding events.

Group   DiffDate    eventNumber
58390   0           0
58390   1765        0
24979   0           0
24979   61          0
24979   84          0
24979   1003        0
24979   1095        0

For final evaluation I need the serial number of the events by group, like this:

Group   DiffDate    eventNumber
58390   0           0
58390   1765        1
24979   0           0
24979   61          1
24979   84          2
24979   1003        3
24979   1095        4

Any Ideas?

No need in `plyr`, just do `with(df, ave(Group, Group, FUN = seq)) - 1L` — David Arenburg, May 10 '15 at 19:40

Max Candocia · Answer 1 · 2015-05-10T19:52:24.040

0

You can do

library(plyr)
ddply(data,.(Group),function(x) x$eventNumber = 0:(nrow(x)-1))

This is provided that they're all sorted. If they're not, you can just do that in the function in ddply.

edited May 10 '15 at 19:52

answered May 10 '15 at 19:29

Max Candocia

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32
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This won't reach the exact desired output. – David Arenburg May 10 '15 at 19:40

score 0 · Accepted Answer · answered May 10 '15 at 21:02

0

Try:

library(dplyr)
df %>% group_by(Group) %>% mutate(eventNumber = row_number()-1)

answered May 10 '15 at 21:02

Steven Beaupré

20,785
7
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Works perfectly, thanks so much – Thomas Eigentler May 11 '15 at 09:06

number of identical ids in a data frame

2 Answers2