I have a dataframe like this:
df <- data.frame("subj.no" = rep(1:3, each = 24),
"trial.no" = rep(1:3, each = 8, length.out = 72),
"item" = c(rep(c("ball", "book"), 4), rep(c("doll", "rope"), 4), rep(c("fish", "box"), 4), rep(c("paper", "candle"), 4), rep(c("horse", "marble"), 4), rep(c("doll", "rope"), 4), rep(c("tree", "dog"), 4), rep(c("ball", "book"), 4), rep(c("horse", "marble"), 4)),
"rep.no" = rep(1:4, each = 2, length.out = 72),
"DV" = c(1,0,1,0,1,0,0,1,1,0,1,0,0,0,1,0,1,0,1,0,1,0,0,0,0,1,1,1,1,0,0,1,0,1,1,0,0,1,0,1,1,1,0,1,0,0,
1,0,0,1,1,0,1,0,0,1,1,1,1,0,0,0,0,0,0,1,0,1,0,1,1,0),)
I now want to create another column DV.no which says that the value 1 occurred the nth time within that combination of subj.no, trial.no and item. For DV==0, the value in the new column should be 0.
So the resulting vector should look like this:
DV.no = c(1,0,2,0,3,0,0,1,1,0,2,0,0,0,3,0,1,0,2,0,3,0,0,0,0,1,1,2,2,0,0,3,0,1,1,0,0,2,0,3,1,1,0,2,0,0,2,0,0,1,1,0,2,0,0,2,1,1,2,0,0,0,0,0,0,1,0,2,0,3,1,0)
So basically, for each unique combination of values in subj.no, trial.no and item, whenever the value of DV is 1, then 1 should be added to the count in the new variable.
(Remark: The column rep.no is not part of the relevant value combination. But it's in the df anyway, and since I didn't know if it's useful for the solution, I left it there.)
How can this be done in R?
We can do a group by cumsum on the 'DV' column
library(dplyr)
df %>%
group_by(subj.no, trial.no, item) %>%
mutate(V.no = cumsum(DV)* DV)
Or in base R with ave
df$V.no <- with(df, DV *ave(DV, subj.no, trial.no, item, FUN = cumsum))
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