CODEWITHSUNDEEP
rmatrixvector
Shuo
Shuo

Reputation: 491

R - testing matrix values based on vector

I have a matrix

blah <- structure(c(10L, 7L, 5L, 3L, 8L, 10L, 3L, 9L, 3L, 3L, 4L, 8L, 7L, 4L, 8L, 5L, 2L, 1L, 9L, 7L, 6L, 7L, 9L, 3L, 3L), .Dim = c(5L, 5L))

> blah
     [,1] [,2] [,3] [,4] [,5]
[1,]   10   10    4    5    6
[2,]    7    3    8    2    7
[3,]    5    9    7    1    9
[4,]    3    3    4    9    3
[5,]    8    3    8    7    3

I have a set of vectors corresponding to the maximum values for each column.

max <- apply(blah,2,max)
> max
[1] 10 10  8  9  9

I want to return a logical vector based on the largest value per column

     [,1] [,2] [,3] [,4] [,5]
[1,]    T    T    F    F    F
[2,]    F    F    T    F    F
[3,]    F    F    F    F    T
[4,]    F    F    F    T    F
[5,]    F    F    T    F    F

I know I can implement a loop over the columns to do this, but is there an elegant R-type way to accomplish this?

Upvotes: 1

Views: 69

Answers (1)

Shuo
Shuo

Reputation: 491

apply(blah,2,function(x) {x == max(x)})

This just hit me. It's so simple. Can't believe I didn't think of this earlier.

Upvotes: 4

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