Data frame vs matrix quirk: Hinky error message?

P.S.

The way the logical matrix is constructed is NOT general purpose.
Quoting myself quoting Bert,

Actually, it works, as long as the logical index matrix has the same
dimensions as the data frame.

zmat <- matrix(1:12,nr=4)
zdf <- data.frame(zmat)

# Numeric index matrix.
ix <- cbind(1:2,2:3)
# Logical index matrix.
ix2 <- row(zdf) == ix[, 1] & col(zdf) == ix[, 2]

Here the number of rows in zdf is a multiple of the vectors ix[, 1] and ix[
, 2] lengths.
The recycling rules makes it work. But if the numeric index matrix has, say,
3 rows,
another way of constructing the logical one would be needed.

jx <- cbind(1:3, c(2:3, 3))
row(zdf) == jx[, 1] & col(zdf) == jx[, 2]
      [,1]  [,2]  [,3]
[1,] FALSE FALSE FALSE
[2,] FALSE FALSE FALSE
[3,] FALSE FALSE FALSE
[4,] FALSE FALSE FALSE

(Anyway, I don't believe that was the point.)

R.B.



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