Custom function for multiplying all odd values in matrix

user_17326883 0
Viewed 66

I am trying to code a function in R which takes one argument (matrix) and multiply all odd values in it by 0.618.

This is what I got so far, but it is my first time working with R matrixes and not sure how to replace values in for loop, or if it's better to do it after multiplying numbers.

r for-loop matrix
4 Answers

You can try the code below

mat <- matrix(1:12, 3, 4)
mat2 <- mat * 0.618^(mat %% 2)

where

  • %% checks the modulo over 2
> mat %% 2
     [,1] [,2] [,3] [,4]
[1,]    1    0    1    0
[2,]    0    1    0    1
[3,]    1    0    1    0
  • 0.618^(...) gives the coefficient
> 0.618^(mat %% 2)
      [,1]  [,2]  [,3]  [,4]
[1,] 0.618 1.000 0.618 1.000
[2,] 1.000 0.618 1.000 0.618
[3,] 0.618 1.000 0.618 1.000
user_121587570 
mat <- matrix(1:12, 3, 4)

mat[mat %% 2 != 0L] <- 0.618 * mat[mat %% 2 != 0L]
mat
#       [,1] [,2]  [,3]   [,4]
# [1,] 0.618 4.00 4.326 10.000
# [2,] 2.000 3.09 8.000  6.798
# [3,] 1.854 6.00 5.562 12.000

Using magrittr to avoid repitition:

library(magrittr)
mat[mat %% 2 != 0L] %<>% {0.618 * .}
user_45522950

Try this:

mat <- matrix(sample(80), ncol = 10)

ifelse(mat %% 2 != 0, mat * 0.618, mat)

ifelse takes three arguments:

  1. the condition (in your case that the number is divisible by 2)

  2. the value to assign if the condition occurs

  3. the value to be assigned if the condition does not occur

user_149765800

function oddMult takes matrix A and multiplication value v and multiplies odd values within matrix A with v:

oddMult <- function(A, v){
  
  indices <- which(A %% 2 == 1)
  A[indices] <- A[indices] * v
  
  A
}

Example:

set.seed(21)
A <- matrix(sample(20, 50, TRUE), 10, 5)
oddMult(A, 0.618)

        [,1]   [,2]   [,3]   [,4]   [,5]
 [1,] 20.000  4.326  6.798  3.090 18.000
 [2,] 10.506 16.000  3.090  2.000 11.742
 [3,]  3.090  4.000 20.000 18.000  3.090
 [4,] 14.000  9.270  5.562 14.000  8.000
 [5,]  4.326 18.000  8.000  9.270  9.270
 [6,]  6.798 18.000 16.000 16.000  9.270
 [7,] 11.742  1.854  5.562 16.000 16.000
 [8,]  4.000  8.034  0.618  1.854  6.000
 [9,]  5.562  6.798  1.854  5.562 16.000
[10,] 10.000  6.798  1.854 12.000  6.000
user_121484020
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