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I want to sort month names. When I use the strptime function it returns an error as the attribute values only contains month names. When I use the sort function, the months are sorted alphabetically.

Joe Doyle
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shridatt
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2 Answers2

35

You could always convert your data to a factor. For example, suppose we have

x = c("January", "February", "March", "January")

then to convert to a factor, we have:

x_fac = factor(x, levels = month.name)

which on sorting gives:

R> sort(x_fac)
[1] January  January  February March   
12 Levels: January February March April May June July August ... December
csgillespie
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    Constants `month.name` and `month.abb` are useful in this regard so you don't need to type out the month names etc. Only useful for English month names and abbreviations though. – Gavin Simpson Mar 19 '12 at 12:10
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    also, be careful with "Feburary" -- you're unlikely (I hope) to find it in the real data. Maybe that was part of the reason for @GavinSimpson's suggestion – Ben Bolker Mar 19 '12 at 12:20
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    Thanks @GavinSimpson I didn't know about `month.name` – csgillespie Mar 19 '12 at 13:04
4

This is crude but if you wanted to make a function to sort or order rows by a month this would work:

sort.month <- function(x, dataframe = NULL){
    y <- data.frame(m1 = month.name, m2 = month.abb, n = 1:12)
    z <- if(max(nchar(x)) == 3) match(x, y[, 'm2']) else match(x, y[, 'm1'])
    x <- if(is.null(dataframe)) x else dataframe
    h <- data.frame(z, x)
    h[order(z), ][, -1]
}

#examples
x <- sample(month.name, 20, r=T)
a<-data.frame(y= x, k =1:20, w=letters[1:20])
sort.month(a$y, a)
sort.month(a$y)
Tyler Rinker
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  • I use this type of sorting a lot inside the custom functions I create - so I prefer this approach over the minimalist or standard approach posted by @csgillespie (i.e. my vote goes here). – SilSur Oct 06 '21 at 09:59
  • @SilSur at first I rejected the edit you suggested, but after considering more your suggestion was safe to assume internally. I manually edited the post to match your suggested edits as it was too late once I rejected it. – Tyler Rinker Oct 06 '21 at 13:18
  • ...so no brownie points for my edit? – SilSur Oct 06 '21 at 14:03
  • Sorry no :-( I am the worst. I got this new power to approve edits and screwed it up my very first time. With great power comes great responsibility. – Tyler Rinker Oct 06 '21 at 17:48