替换列名和行名相同的数据帧单元格值

Question

I'm interested in finding a way to replace cells in an R data frame that have the same column and row name. This is because I'm comparing the minimum distance between spatial objects and it is not useful to compare objects to themselves. For example, where both column name is "3" and row name is "3", the current value should be replaced with "NA".

I've been playing around with if statements but think there must be a simpler way to do this that I'm overlooking. I'm relatively new to coding so would appreciate sample code and an explanation.

Answer 1

Using @SimonJackson's data:

d[cbind(seq_len(nrow(d)), match(rownames(d),colnames(d)))] <- NA

Simply match the rownames to the colnames and then replace using a matrix index.

If the rownames and colnames are in the same order in a square matrix/data.frame, then just:

diag(d) <- NA

...will do it.

Answer 2

Here's a custom function, replace_matching() to do the job. It will even let you adjust what to insert in the cells:

Here's some toy data...

d <- data.frame(a = 1:10)
for (i in 2:10) {
  d[[letters[i]]] <- 1:10
}
rownames(d) <- letters[10:1]
d
#>    a  b  c  d  e  f  g  h  i  j
#> j  1  1  1  1  1  1  1  1  1  1
#> i  2  2  2  2  2  2  2  2  2  2
#> h  3  3  3  3  3  3  3  3  3  3
#> g  4  4  4  4  4  4  4  4  4  4
#> f  5  5  5  5  5  5  5  5  5  5
#> e  6  6  6  6  6  6  6  6  6  6
#> d  7  7  7  7  7  7  7  7  7  7
#> c  8  8  8  8  8  8  8  8  8  8
#> b  9  9  9  9  9  9  9  9  9  9
#> a 10 10 10 10 10 10 10 10 10 10

The function...

replace_matching <- function(df, replace_with = NA) {
  # Find all combinations of row and column names
  name_grid <- expand.grid(rownames(df), colnames(df), stringsAsFactors = FALSE)

  # Find any names with matches
  matched_names <- name_grid$Var1[name_grid$Var1 == name_grid$Var2]

  # Wherever there are matches, set cell to NA
  for (mn in matched_names) {
    df[mn, mn] <- replace_with
  }

  return(df)
}

Default use case...

replace_matching(d)
#>    a  b  c  d  e  f  g  h  i  j
#> j  1  1  1  1  1  1  1  1  1 NA
#> i  2  2  2  2  2  2  2  2 NA  2
#> h  3  3  3  3  3  3  3 NA  3  3
#> g  4  4  4  4  4  4 NA  4  4  4
#> f  5  5  5  5  5 NA  5  5  5  5
#> e  6  6  6  6 NA  6  6  6  6  6
#> d  7  7  7 NA  7  7  7  7  7  7
#> c  8  8 NA  8  8  8  8  8  8  8
#> b  9 NA  9  9  9  9  9  9  9  9
#> a NA 10 10 10 10 10 10 10 10 10

Changing default replacement value to -99...

replace_matching(d, -99)
#>     a   b   c   d   e   f   g   h   i   j
#> j   1   1   1   1   1   1   1   1   1 -99
#> i   2   2   2   2   2   2   2   2 -99   2
#> h   3   3   3   3   3   3   3 -99   3   3
#> g   4   4   4   4   4   4 -99   4   4   4
#> f   5   5   5   5   5 -99   5   5   5   5
#> e   6   6   6   6 -99   6   6   6   6   6
#> d   7   7   7 -99   7   7   7   7   7   7
#> c   8   8 -99   8   8   8   8   8   8   8
#> b   9 -99   9   9   9   9   9   9   9   9
#> a -99  10  10  10  10  10  10  10  10  10