Apply function to all even values in data frame-CodePudding

df <- as.data.frame(matrix(1:5, rep(10), ncol = 10))

This is my example data frame. I'd like to apply the following to all even values: take -6 and then compute the absolute value.

The result should look like that:

   V1 V2 V3 V4 V5 V6 V7 V8 V9 V10
1   1  1  1  1  1  1  1  1  1   1
2   4  4  4  4  4  4  4  4  4   4
3   3  3  3  3  3  3  3  3  3   3
4   2  2  2  2  2  2  2  2  2   2
5   5  5  5  5  5  5  5  5  5   5
6   1  1  1  1  1  1  1  1  1   1
7   4  4  4  4  4  4  4  4  4   4
8   3  3  3  3  3  3  3  3  3   3
9   2  2  2  2  2  2  2  2  2   2
10  5  5  5  5  5  5  5  5  5   5

You could also say replace all the 2s by 4s and vice versa....

I tried to filter() out all the evens and then do -6 and abs(), tried a for loop as well and an if else function... It didn't work out the way I wanted and got far too complicated

CodePudding user response：

We could directly apply the function as these are vectorized

df[!df %%2] <- abs(df[!df %%2]-6)

-output

> df
   V1 V2 V3 V4 V5 V6 V7 V8 V9 V10
1   1  1  1  1  1  1  1  1  1   1
2   4  4  4  4  4  4  4  4  4   4
3   3  3  3  3  3  3  3  3  3   3
4   2  2  2  2  2  2  2  2  2   2
5   5  5  5  5  5  5  5  5  5   5
6   1  1  1  1  1  1  1  1  1   1
7   4  4  4  4  4  4  4  4  4   4
8   3  3  3  3  3  3  3  3  3   3
9   2  2  2  2  2  2  2  2  2   2
10  5  5  5  5  5  5  5  5  5   5

CodePudding user response：

You could use ifelse inside an lapply, and write the resultant list back into the data frame:

df <- as.data.frame(matrix(1:5, rep(10), ncol = 10))

df[] <- lapply(df, function(x) ifelse(x %% 2 == 0, abs(x - 6), x))

df
#>    V1 V2 V3 V4 V5 V6 V7 V8 V9 V10
#> 1   1  1  1  1  1  1  1  1  1   1
#> 2   4  4  4  4  4  4  4  4  4   4
#> 3   3  3  3  3  3  3  3  3  3   3
#> 4   2  2  2  2  2  2  2  2  2   2
#> 5   5  5  5  5  5  5  5  5  5   5
#> 6   1  1  1  1  1  1  1  1  1   1
#> 7   4  4  4  4  4  4  4  4  4   4
#> 8   3  3  3  3  3  3  3  3  3   3
#> 9   2  2  2  2  2  2  2  2  2   2
#> 10  5  5  5  5  5  5  5  5  5   5

^{Created on 2022-11-05 with reprex v2.0.2}