Find minimum for every row in a dataframe stemming from a unique column

Question

I need to find the row-wise minimum in an array where each minimum must stem from a unique column. For example, a is a dataframe/matrix

| X1 | X2|X3|
| 4  | 5 | 6|
| 1  | 2 | 3|
| 7  | 8 | 9|

When i use rowMin, the output is 4,1,7. However, what I need an output of is unique minimum of each row vs column. Therefore the output needs to be 5,1,9 I know there are solutions in python, Im unable to do this in R!

Sorry for not being more clear, Because the matching has to be with the minimum in the column and row. So in column 1, 1 is the minimum and so it will be matched with row 2. so then column 1 and row 2 is out of the matching process, so it is then 5 in column 2, row1 — bluejay_vk, May 31 '22 at 18:34

score 3 · Accepted Answer · answered May 31 '22 at 18:34

You could use recursion as follows:

unique_min <- function(mat){
  if(NCOL(mat) == 1) min(mat)
  else c(min(mat[,1]), Recall(mat[-which.min(mat[,1]), -1]))
}
unique_min(df)
[1] 1 5 9

Note that the above is the results of doing columnwise instead of rowwise. If you do it rowwise:

 unique_min(t(df))
 [1] 4 2 9

score 0 · Answer 2 · answered Jun 01 '22 at 20:14

0

Another recursion

f <- function(n) {
    if (n == 1) {
        return(which.min(df[1:n, ]))
    }
    v <- Recall(n - 1)
    c(v, which.min(replace(df[n, ], v, Inf)))
}

df[cbind(f(nrow(df)), 1:ncol(df))]
# [1] 4 2 9

answered Jun 01 '22 at 20:14

ThomasIsCoding

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Find minimum for every row in a dataframe stemming from a unique column

2 Answers2