How to find mode of a multidimensional array in R

Question

I have a multidimensional array

 ,,1
    [,1] [,2]        
 [1,] "0"  "a"    
 [2,] "1"  "a"    
 [3,] "1"  "b"
 [2,] "1"  "c"    
 [3,] "1"  "c"
 ,,2
    [,1] [,2]        
 [1,] "0"  "a"    
 [2,] "1"  "a"    
 [3,] "1"  "a"
 [2,] "0"  "b"    
 [3,] "0"  "c"

i just want to find the mode, if the first column is "1" for every group data. For this multidimensional array, i want output maybe like this

 ,,1
 c
 ,,2
 a

or

[1] c
[2] a    

Answer 1

Suppose your array looks like this:

set.seed(1)
vec <- sample(c(0:3, letters[1:3]), 5 * 2 * 3, replace = TRUE)
dim(vec) <- c(5, 2, 3)
vec
#> , , 1
#> 
#>      [,1] [,2]
#> [1,] "0"  "a" 
#> [2,] "3"  "c" 
#> [3,] "c"  "2" 
#> [4,] "0"  "b" 
#> [5,] "1"  "1" 
#> 
#> , , 2
#> 
#>      [,1] [,2]
#> [1,] "2"  "1" 
#> [2,] "2"  "b" 
#> [3,] "0"  "b" 
#> [4,] "a"  "1" 
#> [5,] "a"  "c" 
#> 
#> , , 3
#> 
#>      [,1] [,2]
#> [1,] "0"  "0" 
#> [2,] "c"  "b" 
#> [3,] "a"  "a" 
#> [4,] "a"  "a" 
#> [5,] "0"  "1"

Then you can find the most common entry in each slice of the array by doing:

apply(vec, 3, function(x) names(rev(sort(table(x))))[1])
#> [1] "c" "b" "a"

^{Created on 2022-02-03 by the reprex package (v2.0.1)}