Summing up values and adding them in to new column-CodePudding

I am completely new at R. How can I sum-up value and create another row based on a condition. Example:

a   b  c   d 
0   a  1  100
0   a  2  300
0   b  3  150
0   b  4  250

after the manipulation, I would get another row that would look like this

a   b  c   d   new_row
0   a  1  100   100
0   a  2  300   400
0   b  3  150   250
0   b  4  250    0

So basically if the b=="a" sum up values in d to make a new_row. but if its b, subtract them.

df<- mutate(df, D = lag(d)   D)

But it says I can't take values from the D column yet. and pointers to a totally noob programmer in R?

CodePudding user response：

You could use cumsum combined with ifelse

library(dplyr)

df %>% 
  mutate(new_col = cumsum(ifelse(b == "b", -d, d)))

to get

# A tibble: 4 x 5
      a b         c     d new_col
  <dbl> <chr> <dbl> <dbl>   <dbl>
1     0 a         1   100     100
2     0 a         2   300     400
3     0 b         3   150     250
4     0 b         4   250       0