Group increase

Question

I am trying to increase the columns for each group. Therefore, if there is a value, we increase it based on the value in front of it, otherwise we will leave it.

So, for example, it will go from df to dfb.

df <- data.frame(group = c("A", "A", "B", "B", "B", "C", "C", "C", "D", "D"), num = c(1, NA, NA, 8, NA, 5, NA, NA, 10, NA)) dfb <- data.frame(group = c("A", "A", "B", "B", "B", "C", "C", "C", "D", "D"), num = c(1, 2, NA, 8, 9, 5, 6, 7, 10, 11)) > df group num 1 A 1 2 A NA 3 B NA 4 B 8 5 B NA 6 C 5 7 C NA 8 C NA 9 D 10 10 D NA > dfb group num 1 A 1 2 A 2 3 B NA 4 B 8 5 B 9 6 C 5 7 C 6 8 C 7 9 D 10 10 D 11 

My best attempt was this, but it did not work

 dfc <- df %>% mutate(num = ifelse(is.na(num),lag(num) + 1, num)) 

Deleted my previous question because my problem was previously poorly defined. Thanks for the help!

Answer 1

We can do it

 df %>% group_by(grp1= cumsum(!is.na(num)), group) %>% mutate(num = if(n() > 1) num[1L] + row_number()-1 else num) %>% ungroup() %>% select(-grp1) # A tibble: 10 × 2 # group num # <fctr> <dbl> #1 A 1 #2 A 2 #3 B NA #4 B 8 #5 B 9 #6 C 5 #7 C 6 #8 C 7 #9 D 10 #10 D 11 

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Or with data.table

 library(data.table) setDT(df)[, num := if(.N >1) num[1L] + seq_len(.N)-1 else num,.(grp1=cumsum(!is.na(num)), group)] 

Answer 2

All you needed was basic for the loop :) cheers!

 df <- data.frame(group = c("A", "A", "B", "B", "B", "C", "C", "C", "D", "D"), num = c(1, NA, NA, 8, NA, 5, NA, NA, 10, NA)) df.new <- df for(i in 2:dim(df.new)[1]){ if(!is.na(df[i - 1, 'num'])){ df.new[i, 'num'] <- df[i - 1, "num"] + 1 }