Count the number of repetitions of a constant variable in R

Question

Consider the following MWE:

df <- data.frame(Day=1:10, Value = c("Yes","No","Yes", "Yes", "Yes", "No", "No", "Yes","Yes", "No")) Day Value 1 Yes 2 No 3 Yes 4 Yes 5 Yes 6 No 7 No 8 Yes 9 Yes 10 No 

I need an extra column that counts the number of times. “Value” is already “yes”. Therefore, when the value is “No”, the new variable should always be 0. If “Yes” appears after “No”, it is set to 1. If subsequent observations are also yes, it should be 2 As soon as the “Yes” chain is intermittent, new the variable for the next "yes" will be again 1. Therefore, my data frame should look like this:

 Day Value Count 1 Yes 1 2 No 0 3 Yes 1 4 Yes 2 5 Yes 3 6 No 0 7 No 0 8 Yes 1 9 Yes 2 10 No 0 

Hope someone can help me.

Answer 1

You can try using "data.table", in particular the rleid function:

Example:

 library(data.table) as.data.table(df)[, count := sequence(.N), by = rleid(Value)][Value == "No", count := 0][] # Day Value count # 1: 1 Yes 1 # 2: 2 No 0 # 3: 3 Yes 1 # 4: 4 Yes 2 # 5: 5 Yes 3 # 6: 6 No 0 # 7: 7 No 0 # 8: 8 Yes 1 # 9: 9 Yes 2 # 10: 10 No 0 

Answer 2

We can use base R We create a grouping variable ("grp") by comparing adjacent elements of the "Value" column and cumsum with a logical index. This can then be used in ave to create a sequence.

 grp <- with(df, cumsum(c(TRUE,Value[-1L]!=Value[-length(Value)]))) df$count <- ave(seq_along(df$Value), grp, FUN=seq_along)*(df$Value=='Yes') df$count #[1] 1 0 1 2 3 0 0 1 2 0