CODEWITHSUNDEEP
r
Ville
Ville

Reputation: 547

R: Calculating the sum of rows with the function apply

I have this matrix mat=matrix(rnorm(15), 1, 15) [1x15] and I want to use the function apply to calculate the sum of rows in matix mat e.g.

    [,1] [,2] [,3] [,4]
[1,]    1    2    3    0  #the sum is then 6

Here is my code: 

mat=matrix(rnorm(15), 1, 15)
apply(mat[,1:15],1,sum)

Here is the error: Error in apply(mat[, 1:15], 1, sum) : dim(X) must have a positive length

If I create two or more rows the apply function works. e.g.

mat=matrix(rnorm(15), 2, 15)
apply(mat[,1:15],1,sum) #this will work

What should I change to the function so it would work even for matrices with one row?

Upvotes: 0

Views: 1626

Answers (3)

Vishnu S Shukla
Vishnu S Shukla

Reputation: 1

create a matrix and use general apply formulation: matrix =m, MARGIN = 1 (for row),2(for column), and FUN = sum.

   m=matrix(1:9,3,3)
   apply(m,1,sum)

Upvotes: 0

IRTFM
IRTFM

Reputation: 263499

Do this instead and then go read the ?Extract help page. That page has a wealth of information about the most fundamental functions of R, namely "[" and "[[".

apply(mat[ ,1:15, drop=FALSE],1,sum)  # preserves the matrix class
[1] -1.621488

Upvotes: 2

Alejandro Andrade
Alejandro Andrade

Reputation: 2216

The problem is that when you call the elements 1 to 15 you are converting your matrix to a vector so it doesn't have any dimension. just using the as.matrix in the apply call will make it work.

mat=matrix(rnorm(15), 1, 15)
apply(as.matrix(mat[,1:15]),2,sum)

Upvotes: 2

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