How to sort alphabetically in R?

Question

My files are of the format:

ada1
ada2
ada3
....
ada10
ada11
ada12

Unfortunately, when I write out a10,a11 and a12 comes before a2. Could you help me sort it alphabetically as it should be?

#

Edit

Now, I have thousands of these files. Basically, xyz1-12, abc1-12 etc.

I use the following to get all files:

GG <- grep("*.txt", list.files(), value = TRUE)

So I can't put 'ada' manually.

What you show is not alphabetical sorting. You can use `mixedsort` from package gtools. — Roland, Apr 18 '14 at 18:38

Matthew Lundberg · Answer 1 · 2014-04-18T18:55:23.193

2

If there are always three characters, you can sort independently by those characters, followed by a numeric sort of the rest of the string:

GG <- paste0(c('ada', 'xyz'), 1:20) # Synthesis of data similar to what your command would give

Using order with multiple arguments gives the permutation of the vector, then indexing by that permutation returns the data in the desired sort order:

GG[order(substring(GG, 1, 3), as.numeric(substring(GG, 4)))]
 [1] "ada1"  "ada3"  "ada5"  "ada7"  "ada9"  "ada11" "ada13" "ada15" "ada17" "ada19" "xyz2"  "xyz4"  "xyz6"  "xyz8"  "xyz10"
[16] "xyz12" "xyz14" "xyz16" "xyz18" "xyz20"

edited Apr 18 '14 at 18:55

answered Apr 18 '14 at 18:40

Matthew Lundberg

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I use GG <- grep("*.txt", list.files(), value = TRUE) to list the files in the folder. How can I "connect" it with your code instead of putting names manually? Thanks a lot! – Geekuna Matata Apr 18 '14 at 18:51
Could you please explain? I didn't get it. Thanks – Geekuna Matata Apr 18 '14 at 18:54
Sorry, I misread your comment. I substituted `GG` in the expression. It sounds like this is what you want. – Matthew Lundberg Apr 18 '14 at 18:56
Sorry, I may not have explained properly. This is not what I was looking for. Basically, GG gives me the names of all the files in the folder, which I want to sort. I don't want to insert 'ada','xyz' manually like you have. How could I do it? Thanks – Geekuna Matata Apr 18 '14 at 18:58
Thanks anyways. Mixed sort is straightforward. – Geekuna Matata Apr 18 '14 at 19:04

score 1 · Accepted Answer · answered Apr 18 '14 at 18:41

1

Another way using package gtools:

require(gtools)
x <- paste0('a', 1:12)
mixedsort(x)
[1] "a1"  "a2"  "a3"  "a4"  "a5"  "a6"  "a7"  "a8"  "a9"  "a10" "a11" "a12"

answered Apr 18 '14 at 18:41

James King

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Thanks. I have added some info. I can't add a manually as I have thousands of files. How can I adapt your code? – Geekuna Matata Apr 18 '14 at 18:49
I don't understand why you can't just use `mixedsort(GG)`. – James King Apr 18 '14 at 18:58
@GeekunaMatata He simply created a set of "test" names. Just run `mixedsort` on your collection of file names. – Carl Witthoft Apr 18 '14 at 18:59

ilir · Answer 3 · 2014-04-18T18:49:12.300

If you can't change their names to something better (that is ada001, ada002...) then you could create an double index. I am assuming fnames is a vector with the file names, and the numbers are only preceded by a fixed number of letters.

alpha <- substr(fnames, 1, 3)
num <- as.integer(substr(fnames, 4, nchar(fnames)))

o <- order(alpha, num)   ## that's your sorting vector

You can modify this procedure to accommodate a varying number of letters using regular expressions to find the split.

score 0 · Answer 4 · edited May 23 '17 at 11:51

If you can change the file names you could do something like the following:

names0 <- paste0("a", 1:20)
temp <- strsplit(names0, "a")
ind <- sapply(temp, "[[", 2)
names1 <- paste0("a", sprintf("%03d", as.numeric(ind)))

> names1
[1] "a001" "a002" "a003" "a004" "a005" "a006"
[7] "a007" "a008" "a009" "a010" "a011" "a012"
[13] "a013" "a014" "a015" "a016" "a017" "a018"
[19] "a019" "a020"

You may have to tweak the call to sprintf, based on this answer.

Just to clarify, using file.rename, it would be pretty easy to rename all your files.

How to sort alphabetically in R?

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