Find the indices of the odd numbers in an integer vector

Question

Say we have some vector:

someVector = c(1, 3, 4, 6, 3, 9, 2, -5, -2)

I want to get a vector that has the locations in someVector of all the odd elements

so in this case it would look like...

resultVector = c(1, 2, 5, 6, 8)

Solution 1

> which(someVector %% 2 == 1)
[1] 1 2 5 6 8

Solution 2

library(schoolmath)
which(is.odd(someVector))
[1] 1 2 5 6 8

just for fun here the code of the is.odd function :

function (x) 
{
  start <- 1
  end <- length(x) + 1
  while (start < end) {
    y <- x[start]
    if (y == 0) {
      cat("Please enter a number > 0")
      end
    }
    test1 <- y/2
    test2 <- floor(test1)
    if (test1 != test2) {
      if (start == 1) {
        result = TRUE
      }
      else {
        result <- c(result, TRUE)
      }
    }
    else {
      if (start == 1) {
        result = FALSE
      }
      else {
        result <- c(result, FALSE)
      }
    }
    start <- start + 1
  }
  return(result)
}

Definitely , Don't use this function !

Comments

[GSee]

Wow! There's a lot of code in that is.odd function. Why is that better than is.odd <- function(x) x %% 2 == 1 ? ... Also, looks like that will be slower since it's growing a vector in a while loop (even though the function already knows the length of the output)

[agstudy]

@GSee you 're right , I saw this mee too I hope I will not dwonvoted for this stupid function :)

[GSee]

Look at how ugly this is: suppressMessages(is.odd(c(0, 2, 0, 1, 0))). Wonder why the author doesn't accept that 0 is even. en.wikipedia.org/wiki/Parity_of_zero

[agstudy]

@GSee really dirty and ugly:)tha's said , it the school package. The idea maybe to show the algorithm (implements the modulo division)

[flodel]

+1 for "don't use this function!". It is so ugly it is funny.

[Marjolein Fokkema]

Exactly what an odd function should look like