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I have been struggling to solve this apparently easy problem, I have a data frame with the following column names:

  names <-  c("2013-1", "2013-10", "2013-11", "2013-12", "2013-2", 
"2013-3", "2013-4", "2013-5", "2013-6", "2013-7", "2013-8", "2013-9", 
"2014-1", "2014-2", "2014-3")

As you can see, the column names are dates (recognized by R as character) and I need to reorder the columns so each column corresponds to the month that comes after the previous one, eg. 2013-1, 2013-2, 2013-3... but since R sees the column names as words and not dates it is ordering it differently, with 2013-10 before 2013-2 for example.

I tried to convert the column names to date using:

as.Date(names, format="%Y-%m")

But R apparently does not recognize this date format and I get NA's. I am still stuck with this ordering no matter what I try so any help would be very appreciated.

Thank you

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2 Answers 2

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2

You may also have a look at as.yearmon in zoo package. From the help text: "yearmon is a class for representing monthly data."

library(zoo)
x <- as.yearmon(names, format = "%Y-%m")
x

# sort and format output according to taste, e.g.
format(sort(x), "%Y-%m")
# [1] "2013-01" "2013-02" "2013-03" "2013-04" "2013-05" "2013-06" "2013-07" "2013-08" "2013-09"
# [10] "2013-10" "2013-11" "2013-12" "2014-01" "2014-02" "2014-03"
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Thanks, chose it as answer because solves my problem faster and in a cleaner way.
2

Try

as.Date(paste(names, "-01", sep=""), format="%Y-%m-%d")

and R should see it as a date.

EDIT: If you want to keep your original format, but insert a zero between 1 and 9, you can use strftime:

strftime(as.Date(paste(names, "-01", sep=""), "%Y-%m-%d"), "%Y-%m")
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It works, but not exactly as I wanted. Adding manually the day means there is no way that R understands yyyy-mm date format? If possible I would prefer to keep the original format.

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