dcast for huge dataframe [R]

问题

Assume a DF of:

    pnr <- c(1, 1, 1, 2, 2, 3, 4, 5, 5)
    diag <- c("a", "a", NA, "b", "a", NA, "c", "a", "f")
    year <- rep(2007, 9)
    ht <- data.frame(pnr, diag, year)

Now I need to reshape such that:

    require(reshape2)
    md <- melt(ht, id = c("pnr", "year"))
    output <- dcast(md, pnr ~ value)

Output is now in the format I want. But when I run this on a large data frame, 13million rows, it will crash R-studio. Is there some smart way to split a dataframe, do the dcast, and tie back?

EDIT : The solutions posted below, will not work in this case, as I not able to install. Surely there is some way to work around this?

回答1:

The easy solution to this case turned out to be switching back to the old reshape package. Which means useing cast instead of dcast. Arun's comments are highly usable, providede one can actually update. Related

来源：https://stackoverflow.com/questions/28986836/dcast-for-huge-dataframe-r