I would like to use the succinctness of magrittr and dplyr to copy single values between rows in a subset of columns based on the values in other columns. This is a simple example; I want to apply this idea to many columns of a large dataset with multiple conditions within a long pipe of commands.
Take the dataframe df <- data.frame(a = 1:5, b = 6:10, x = 11:15, y = 16:20):
a b x y
1 6 11 16
2 7 12 17
3 8 13 18
4 9 14 19
5 10 15 20
For the row where a = 5, I would like to replace the values of x and y with those in the row where b = 7, to give:
a b x y
1 6 11 16
2 7 12 17
3 8 13 18
4 9 14 19
5 10 12 17
This attempt fails:
foo <- function(x){ifelse(df$a == 5, df[df$b == 7, .(df$x)], x)}
df %<>% mutate_each(funs(foo), x, y)
The closest I can get is:
bar <- function(x){ifelse(df$a == 5, df[df$b == 7, "x"], x)}
df %<>% mutate_each(funs(bar), x, y)
but this is incorrect as it replaces both values with the value from x, rather than x and y respectively.
Thanks for the advice.
You could do it using mutate_each and replace:
df %>% mutate_each(funs(replace(., a==5, nth(., which(b==7)))), x, y)
Output:
a b x y
1 1 6 11 16
2 2 7 12 17
3 3 8 13 18
4 4 9 14 19
5 5 10 12 17
Or as per @docendodiscimus 's comment it can be shortened further to (and probably [ is also better than which):
df %>% mutate_each(funs(replace(., a==5, .[b==7])), x, y)