CODEWITHSUNDEEP
r
MDe
MDe

Reputation: 2508

Sort a data.frame by multiple columns whose names are contained in a single object?

I want to sort a data.frame by multiple columns, ideally using base R without any external packages (though if necessary, so be it). Having read How to sort a dataframe by column(s)?, I know I can accomplish this with the order() function as long as I either:

  1. Know the explicit names of each of the columns.
  2. Have a separate object representing each individual column by which to sort.

But what if I only have one vector containing multiple column names, of length that's unknown in advance?

Say the vector is called sortnames.

data[order(data[, sortnames]), ] won't work, because order() treats that as a single sorting argument.

data[order(data[, sortnames[1]], data[, sortnames[2]], ...), ] will work if and only if I specify the exact correct number of sortname values, which I won't know in advance.

Things I've looked at but not been totally happy with:

  1. eval(parse(text=paste("data[with(data, order(", paste(sortnames, collapse=","), ")), ]"))). Maybe this is fine, but I've seen plenty of hate for using eval(), so asking for alternatives seemed worthwhile.
  2. I may be able to use the Deducer library to do this with sortData(), but like I said, I'd rather avoid using external packages.

If I'm being too stubborn about not using external packages, let me know. I'll get over it. All ideas appreciated in advance!

Upvotes: 9

Views: 7231

Answers (1)

mpiktas
mpiktas

Reputation: 11518

You can use do.call:

data<-data.frame(a=rnorm(10),b=rnorm(10)) 
data<-data.frame(a=rnorm(10),b=rnorm(10),c=rnorm(10))
sortnames <- c("a", "b")
data[do.call("order", data[sortnames]), ]

This trick is useful when you want to pass multiple arguments to a function and these arguments are in convenient named list.

Upvotes: 9

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