Data checking function to check if the contents of two variables have a 1:1 mapping

isOneToOne(x, y)

checkIsOneToOne(x, y)

## Arguments

x first variable second variable

## Value

logical: TRUE if 1:1 mapping, FALSE otherwise

## Background

This is a little utility function that I use from time to time when I want to check whether two variables have a one to one mapping they should have. Typically this is where one of them is a short code say variable x, for the other, say variable y. If you have two vectors, one of the short codes, x, and one of the longer, y, they should have a perfect 1:1 mapping, so for any value in x there must the same number of its mapped value in y. For example:

 x y 1 Male 2 Female 3 Other 2 Female 2 Female 1 Male 3 Other Has a perfect 1:1 mapping of x to y so, assuming that I had x and y as vectors, isOneToOne(x, y) will return TRUE.
 x y 1 Male 2 Feemale 3 Other 2 Female 2 Female 1 male 3 Other does not 1:1 (and isn't a completely mad example of typical messes in real world data, if perhaps a very simple one!) Of course, here isOneToOne(x, y) will return FALSE.

## Acknowledgements

I found this nice way of doing this at https://stackoverflow.com/questions/52399474/check-if-variables-are-in-a-one-to-one-mapping

## History/development log

Started before 5.iv.21

Other data checking functions: checkAllUnique(), getNNA(), getNOK()

Chris Evans

## Examples

if (FALSE) {
### this should map OK
isOneToOne(1:5,letters[1:5])
### 1:1 doesn't actually mean just one of each,
### just that the mapping is 1:1!
isOneToOne(rep(1:5, 2), rep(letters[1:5], 2))
### should throw an error as unequal length
isOneToOne(1:26, letters[1:25])
### but this is OK
isOneToOne(1:26, c("1", letters[1:25]))
### but this is not as it's no longer 1:1
isOneToOne(c(1, 1:26), c("1", letters[1:25], "1"))
### same the other way around (essentially)
isOneToOne(1:26,c("a",letters[1:25]))
}