CODEWITHSUNDEEP
r
user
user

Reputation: 1

Writing a function that accepts a vector of integers and returns a logical vector

I have stumbled upon a question I am struggling to tackle.

"Write a function that accepts a vector of integers and returns a logical vector that is TRUE whenever the input is even, FALSE whenever the input is odd and NA whenever the input is nonfinite (that is if it is Inf, -Inf, NA, NaN). Check that it works with positive, negative, zero and nonfinite inputs."

f <- function(x,y)
{
  if (x==Inf)
  {
    print ("NA")
  }else 
    if(x%%2=0)
{print ("TRUE")
    }else
        {print("FALSE")}
  if (y==Inf)
    {print("NA")
    }
  else
    if (y%%2==0)
  {print ("TRUE")
  } else
  {print ("FALSE")
  }
  print(c(x+y, x-y, x^4-y^3, x^2+y^2, y*x))
}

Through my eyes I cannot see where I have gone wrong. I receive an error code saying "Error: unexpected '}' in "}""

Any guidance would be greatly appreciated.

Upvotes: 0

Views: 994

Answers (2)

Tim Biegeleisen
Tim Biegeleisen

Reputation: 522471

The problem with your current approach is that you are trying to operate on a vector, but your if - else logic is really meant to operate on scalars (i.e. single values). I recommend using a vectorized solution, such as the ifelse() function. We could chain together a bunch of calls to ifelse, but it might be easier here to use case_when from the dplyr package:

library(dplyr)

f <- function(x) {
    result <- case_when(
        x %% 2 == 0 ~ TRUE,
        x %% 2 == 1 ~ FALSE,
        is.infinite(x) ~ NA,
        is.nan(x) ~ NA,
        TRUE ~ NA
    )

    return(result)
}

Edit:

I rather like the answer by @markus, which may be exactly what your teacher is expecting. But using case_when as I have above makes the mapping you are expecting explicit. So, from a code clarity point of view, it is completely clear what is going on.

Upvotes: 1

markus
markus

Reputation: 26363

You could shorten your function a bit and write

f <- function(x) { x %% 2 == 0 }

Test

f(c(1:6, Inf, -Inf, NA, NaN))
# [1] FALSE  TRUE FALSE  TRUE FALSE  TRUE    NA    NA    NA    NA

Upvotes: 2

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