问题
I have a df like
ProjectID Dist
1 x
1 y
2 z
2 x
2 h
3 k
.... ....
I want to add a third column such that we have an incrementing counter for each ProjectID:
ProjectID Dist counter
1 x 1
1 y 2
2 z 1
2 x 2
2 h 3
1 k 3
.... ....
I've had a look at seq rank and a couple of other bits particularly looking to see if I could use ddply to help:
df$counter <- ddply(df,.(projectID), function(x).....? )
I think I could adapt this answer How to create a counter/numeration by group? but would prefer something using something like ddply (I can't find an equivalent of cumsum but I think that's the same principle here: Create ascending series of integers by group in Pandas ). That'd let me index occurrences in a list (and e.g. merge on this).
回答1:
A dplyr solution is quite simple:
library(dplyr)
df %>% group_by(ProjectID) %>% mutate(counter = row_number(ProjectID))
# ProjectID Dist counter
#1 1 x 1
#2 1 y 2
#3 2 z 1
#4 2 x 2
#5 2 h 3
#6 1 k 3
来源：https://stackoverflow.com/questions/28647954/add-an-index-or-counter-to-a-dataframe-by-group-in-r