[External] conditional replacement of elements of matrix with another matrix column

A

[,1] [,2]
 [1,]   12   NA
 [2,]   12   NA
 [3,]   12   NA
 [4,]   13   NA
 [5,]   13   NA
 [6,]   13   NA
 [7,]   14   NA
 [8,]   14   NA
 [9,]   14   NA

B

[,1] [,2]
 [1,]   11    6
 [2,]   11    7
 [3,]   11    8
 [4,]   13    9
 [5,]   13   10
 [6,]   13   11
 [7,]   14   12
 [8,]   14   13
 [9,]   14   14

C

[,1] [,2]
 [1,]   12   NA
 [2,]   12   NA
 [3,]   12   NA
 [4,]   13    9
 [5,]   13   10
 [6,]   13   11
 [7,]   14   12
 [8,]   14   13
 [9,]   14   14

same <- A[,1] == B[,1]
same

[1] FALSE FALSE FALSE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE

A[same,2] <- B[same,2]
A

[,1] [,2]
 [1,]   12   NA
 [2,]   12   NA
 [3,]   12   NA
 [4,]   13    9
 [5,]   13   10
 [6,]   13   11
 [7,]   14   12
 [8,]   14   13
 [9,]   14   14

On Sep 01, 2021, at 16:59, Eliza Botto <eliza_botto at outlook.com> wrote:

dput(A)

structure(c(12, 12, 12, 13, 13, 13, 14, 14, 14, NA, NA, NA, NA,
NA, NA, NA, NA, NA), .Dim = c(9L, 2L))

dput(B)

structure(c(11, 11, 11, 13, 13, 13, 14, 14, 14, 6, 7, 8, 9, 10,
11, 12, 13, 14), .Dim = c(9L, 2L))

dput(C)

structure(c(12, 12, 12, 13, 13, 13, 14, 14, 14, NA, NA, NA, 9,
10, 11, 12, 13, 14), .Dim = c(9L, 2L))