Filling missing values in R matrix using previous value in the same row

January 30, 2024

Consider the following example

before = matrix(c(1, 2, 3, NA, 4, 5, NA, NA, 1), ncol = 3)
after = matrix(c(1, 2, 3, 1, 4, 5, 1, 4, 1), ncol = 3)

The matrix before is the kind of matrix I always deal with in terms of position of missing values, whereas the matrix after is the one I need to get to repeatedly.
Is there any efficient routine?

>Solution :

You can apply na.locf() from {zoo} row-wisely (MARGIN = 1L):

> before = matrix(c(1, 2, 3, NA, 4, 5, NA, NA, 1), ncol = 3)
> after = matrix(c(1, 2, 3, 1, 4, 5, 1, 4, 1), ncol = 3)
> (before2 = t(apply(before, 1L, zoo::na.locf)))
     [,1] [,2] [,3]
[1,]    1    1    1
[2,]    2    4    4
[3,]    3    5    1
> identical(before2, after)
[1] TRUE

Read the documentation, there are plenty of options implemented.
Or write your own function, see here.