How to initialize empty data frame (lot of columns at the same time) in R

Question

I found how to initialize an empty data frame with 3 or 4 dimensions. It's like

df <- data.frame(Date=as.Date(character()),
             File=character(), 
             User=numeric(), 
             stringsAsFactors=FALSE)

However, What's the most effective way to initialize an empty data.frame with a lot of column names. like

mynames <- paste("hello", c(1:10000))

The wrong way I tried is:

df <- data.frame(mynames=numeric())

Thanks a lot beforehand

Related: [*Create an empty data.frame*](http://stackoverflow.com/questions/10689055/create-an-empty-data-frame) — Jaap, May 21 '17 at 09:38

TheComeOnMan · Accepted Answer · 2013-12-10T17:51:51.623

33

Maybe this -

df <- data.frame(matrix(ncol = 10000, nrow = 0))
colnames(df) <- paste0("hello", c(1:10000))

And @joran's suggestion - df <- setNames(data.frame(matrix(ncol = 10000, nrow = 0)),paste0("hello", c(1:10000)))

edited Dec 10 '13 at 17:51

answered Dec 10 '13 at 17:35

TheComeOnMan

12,535
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54

yeah. This sounds right. I guess what I need is a matrix and not a data.frame. Thanks – Wilmer E. Henao Dec 10 '13 at 17:37
5

If you really wanted to force it into one line, you could use `setNames`. – joran Dec 10 '13 at 17:38
@WilmerEHenaoH, consider accepting the answer if it solves the problem. joran, good idea, updated the answer. – TheComeOnMan Dec 10 '13 at 17:52

MichaelChirico · Answer 2 · 2016-05-03T01:25:54.227

I would do this using setDF (or setDT, if you prefer data.table as output) and setnames:

library(data.table)

DF <- setnames(setDF(lapply(integer(1e4), function(...) character(0L))),
               paste0("hello", 1:1e4))
head(names(DF))
# [1] "hello1" "hello2" "hello3" "hello4" "hello5" "hello6"

Both steps (setnames and setDF) are more efficient than the base counterparts, since no copies are made.

A benchmark:

library(microbenchmark)

microbenchmark(times = 1000,
               base = {df <- data.frame(matrix(ncol = 10000, nrow = 0))
               colnames(df) <- paste0("hello", c(1:10000))},
               DT = setnames(setDF(lapply(integer(1e4), 
                                          function(...) character(0L))),
                             paste0("hello", 1:1e4)))
# Unit: milliseconds
#  expr      min       lq     mean   median       uq      max neval cld
#  base 26.77218 30.94223 37.30173 36.76721 37.80338 102.2379  1000   b
#    DT 16.68004 23.18865 30.60573 29.18421 36.03590 178.1045  1000  a

How to initialize empty data frame (lot of columns at the same time) in R

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