匹配的rownames等于colnames（对称或非对称矩阵）

Question

I'm doing a statistical analyses on distance matrices in R and want to compare distances within individuals and between groups. I have a matrix where some of the colnames are equal to some of the rownames. I want to extract the values where this criteria is met (the problem is getting it to work on a asymmetric matrix). If the code could save a matrix with logical values where the criteria is met it would be great)

An example of a smaller matrix is shown below:

       1         2         3         4
1 0.4966143 0.8359290 0.7319204 0.7579902
3 0.7002979 0.8621343 0.5152356 0.7875813
4 0.7406555 0.8371479 0.7103873 0.5530200

I want it to end up like this

       1         2         3         4
1    TRUE      FALSE     FALSE     FALSE
3   FALSE      FALSE     TRUE      FALSE
4   FALSE      FALSE     FALSE      TRUE

Would be happy if I could do it without any loops, just vectorized code

Answer 1

We can use outer

out <- outer(row.names(m1), colnames(m1), `==`)
dimnames(out) <- dimnames(m1)
out
#     1     2     3     4
#1  TRUE FALSE FALSE FALSE
#3 FALSE FALSE  TRUE FALSE
#4 FALSE FALSE FALSE  TRUE

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Or rep licate the rownames and column names to make the length s equal and then do a ==

`dim<-`(row.names(m1)[row(m1)] == colnames(m1)[col(m1)], dim(m1))

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NOTE: as @NelsonGon suggested, when we read data ( read.table/read.csv etc.) as a data.frame , the column names can get appended with prefix X as these are non-canonical names ie starting with number. To avoid that either use check.names = FALSE argument in the read.table/read.csv or post process by changing the column names

outer(row.names(df), sub("^X","",names(df)),"==")

assuming 'df' is the data.frame identifier object

data

m1 <- structure(list(`1` = c(0.4966143, 0.7002979, 0.7406555), 
                     `2` = c(0.835929,  0.8621343, 0.8371479), 
                     `3` = c(0.7319204, 0.5152356, 0.7103873), 
                     `4` = c(0.7579902, 0.7875813, 0.55302)), 
                class = "data.frame", 
                row.names = c("1", "3", "4"))