How to remove empty cells and reduce columns - r

Question

I have a table, that looks roughly like this:
| variable | observer1 | observer2 | observer3 | final |
| -------- | --------- | --------- | --------- | ----- |
| case1 | | | | |
| var1 | 1 | 1 | | |
| var2 | 3 | 3 | | |
| var3 | 4 | 5 | | 5 |
| case2 | | | | |
| var1 | 2 | | 2 | |
| var2 | 5 | | 5 | |
| var3 | 1 | | 1 | |
| case3 | | | | |
| var1 | | 2 | 3 | 2 |
| var2 | | 2 | 2 | |
| var3 | | 1 | 1 | |
| case4 | | | | |
| var1 | 1 | | 1 | |
| var2 | 5 | | 5 | |
| var3 | 3 | | 3 | |
Three colums for the observers, but only two are filled.
First I want to compute the IRR, so I need a table that has two columns without the empty cells like this:
| variable | observer1 | observer2 |
| -------- | --------- | --------- |
| case1 | | |
| var1 | 1 | 1 |
| var2 | 3 | 3 |
| var3 | 4 | 5 |
| case2 | | |
| var1 | 2 | 2 |
| var2 | 5 | 5 |
| var3 | 1 | 1 |
| case3 | | |
| var1 | 2 | 3 |
| var2 | 2 | 2 |
| var3 | 1 | 1 |
| case4 | | |
| var1 | 1 | 1 |
| var2 | 5 | 5 |
| var3 | 3 | 3 |
I try to use the tidyverse packages, but I'm not sure. Some 'ifelse()' magic may be easier.
Is there a clean and easy method to do something like this? Can anybody point me to the right function to use? Or just to a keyword to search for on stackoverflow? I found a lot of methods to remove whole empty columns or rows.
Edit: I removed the link to the original data. It was unnecessary. Thanks to Lamia for his working answer.

Answer 1

Out of your 3 columns observer1, observer2 and observer3, you sometimes have 2 non-NA values, 1 non-NA value, or 3 NA values.
If you want to merge your 3 columns, you could do:
res = data.frame(df$coding,t(apply(df[paste0("observer",1:3)],1,function(x) x[!is.na(x)][1:2])))
The apply function will return for each row the 2 non-NA values if there are 2, one non-NA value and one NA if there is only one value, and two NAs if there is no data in the row.
We then put this result in a dataframe with the first column (coding).