= Solution
Compare every complete row with the given <vector>, returning as soon as a match is found. The length check prevents recycling of the <vector>; `seq_len` also handles an empty <matrix> correctly. This implementation treats a missing comparison as a nonmatch and always returns a Boolean.
``
row.match <- function(X, y) {
stopifnot(is.matrix(X), length(y) == ncol(X))
for (i in seq_len(nrow(X))) {
eq <- X[i, ] == y
if (all(!is.na(eq) & eq)) return(TRUE)
}
FALSE
}
``
For the integer-coordinate matrices used below there are no missing values, so this is ordinary exact row equality.
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