Find and print out rownames with missing values in matrix with apply in R

Question

I have a matrix with missing values. Now I would like to find the missing values, which I did with this apply command.

missing <- apply(is.na(matrix), 1, which)

It prints me each row name and if there is a missing value or not. But I would like to print only the row names where there are missing values and which ones. So I tried:

 for(i in length(missing) != 0L) {
    print(i)
  }

But this doesn't seem to work.

Answer 1

Create a matrix with some missings

mt <- matrix(sample(c(1:5, NA), 50, replace = TRUE), nrow = 5)

From the question; adjusted object names

miss <- apply(is.na(mt), 1, which)

Detect which entries of miss have length of zero and store the result as a logical vector

miss_row_lgl <- sapply(miss, \(x) length(x) != 0)

Use logical vector to subset miss

miss[miss_row_lgl]
#> [[1]]
#> [1] 1 7 9
#> 
#> [[2]]
#> [1] 7
#> 
#> [[3]]
#> [1] 6
#> 
#> [[4]]
#> [1] 9