Update subset of values in a dataframe column

Question

Here\'s an excerpt of my dataframe:

  x         y     se
  4         a     7.146329
 15         a     8.458633
 17         a     9.286849
 11         b     6         


        

Answer 1

Could use ifelse here. Assuming data frame is named df1:

df1$x <- ifelse(df1$y %in% c("a", "b"), df1$x - 1, df1$x)