check if two columns have a one-to-one relationship in R-CodePudding

Is there any existing R functionality to check if two columns have a one-to-one relationship (regardless of column type).

Example of expected output:

A    B     C
0    'a'   'apple'
1    'b'   'banana'
2    'c'   'apple'

A & B are one-to-one? TRUE

A & C are one-to-one? FALSE

B & C are one-to-one? FALSE

CodePudding user response：

If you match a vector to itself it will return an integer vector giving the first index each unique value occurs at. We can compare these integer vectors directly:

is_one_to_one = function(x, y) {
  xu = match(x, x)
  yu = match(y, y)
  identical(xy, yu)
}

You could then apply this to each pair of columns.

Wrapping it up in a function:

cor_1to1 = function(df) {
  mat = vapply(df, \(x) match(x, x), FUN.VALUE = integer(nrow(df)))
  nm = combn(colnames(mat), m = 2, FUN = paste, collapse = " :: ")
  val = combn(colnames(mat), m = 2, FUN = function(i) {
      identical(mat[, i[1]], mat[, i[2]])
    }, simplify = TRUE)
  setNames(val, nm)
}

# A :: B A :: C B :: C 
#   TRUE  FALSE  FALSE

CodePudding user response：

You can do:

one_to_one <- function(data){
  data[] <- sapply(data, \(x) match(x, x))
  pairs <- t(combn(seq_len(ncol(data)), 2))
  
  cbind(t(matrix(colnames(data)[t(pairs)], nrow = 2)),
        One2One = apply(pairs, 1, function(x) all(Reduce(`==`, data[, x])))) |>
    as.data.frame()
}

test

one_to_one(df)
#  V1 V2 One2One
#1  A  B    TRUE
#2  A  C   FALSE
#3  B  C   FALSE