How do I extract the index or name of the list item within FUN of lapply?

问题

Say I have a list of lists lists:

> lists
$a
[1] "fas"    "asdfas"    "adfaff" ...

$b
[1] "jnfg"   "gfsdgs"    "fdsafa" ...

...

I'd like to export each list into its own csv file with the filename being the list index. I'm trying to do it using lapply instead of a for loop, is that possible? The difficulty for me is how do I extract the list index (or name in this case) out inside of the FUN? For example, if I were to name them randomly I can do this:

lapply(lists, function (x)
       write.table(paste(sample(1:100000000,1), ".csv", sep=""),
                   sep=",", col.names=F, row.names=F))

Edit: Sample dput: http://pastebin.com/a0eEkT1z

Edit2: Shorter sample: (← this one is more sensible)

list(c("Itm2a", "Rplp2", "Arl6ip5", "Crygn", "Znrf1", "Gm5766", 
"D19Ertd652e", "Nkap"), c("Sergef", "2610002I17Rik", "Hjurp", 
"Mns1", "Top3a", "Ldlrap1", "Ube2c", "Cnot3", "Irf6"), c("Fam109a", 
"Rps3a", "Dut", "Atm", "Fancg", "S100a5", "Lpcat2", "Sec23ip"
))

回答1:

You can't. One trick is to use lapply to loop over the names or you can use Map to do something like

Map(function (name, data)
       write.table(data, paste0(name, ".csv"),
                   sep=",", col.names=F, row.names=F)
, names(lists), lists)

回答2:

You can use mapply

mapply(function(name, x) {
    write.table(x, paste0(name, ".csv"), sep=",", col.names=F, row.names=F)
}, names(lists), lists)

Or actually using lapply is also possible

lapply(names(lists), function(name) {
    write.table(lists[name], paste0(name, ".csv"), sep=",", col.names=F, row.names=F)
})

来源：https://stackoverflow.com/questions/25006076/how-do-i-extract-the-index-or-name-of-the-list-item-within-fun-of-lapply

标签

list

lapply