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mikelove/left_join.R

Last active February 27, 2026 15:19
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Compact left_join.DataFrame
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left_join.R
# adapted from DFplyr
# ignoring rownames and GroupedDataFrame functionality...
left_join.DataFrame <- function(x, y, by = NULL, ...) {
if (is.null(by)) {
by <- intersect(names(x), names(y))
if (length(by) == 0) {
rlang::abort("`by` must be supplied when `x` and `y` have no common variables.")
}
message("Joining with `by = ", deparse(by), "`")
}
S4Vectors::merge(x, y, by = by, sort = FALSE, ...)
}
@sa-lee
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sa-lee commented Feb 25, 2026

would something like this work if you just wanted to do a left join without introducing a dependency, you could wrap up the bit where you set up the join to be a helper function but I don't think you need to register a generic for it since you can let S4Vectors::merge handle dispatch?

join_mcols_left <- function(x, y, by = NULL, ...) {
    x_id <- x
    x_id$.id <- factor(seq_along(x))
    if (!is(y, "DataFrame")) {
        y <- DataFrame(y)
    }
    if (is.null(by)) {
        by <- intersect(names(mcols(x_id)), names(y))
        if (length(by) == 0) {
            rlang::abort("`by` must be supplied when `x` and `y` have no common variables.")
        }
        message("Joining with `by = ", deparse(by), "`")
    }
    new_mcols <- S4Vectors::merge(mcols(x_id), y, by = by, sort = FALSE, ...)
    new_mcols <- new_mcols[order(new_mcols$.id), ]
    new_x <- x[as.integer(new_mcols$.id)]
    new_mcols$.id <- NULL
    mcols(new_x) <- NULL
    mcols(new_x) <- new_mcols
    return(new_x)
}

@mikelove
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mikelove commented Feb 27, 2026

thanks! I'll work on adding/testing this next week (my end of week got backed up with deadlines)

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