R help - Apr 2011 - Sorting dataframe by number of occurrences of factor

Apologies for what's probably quite simple, but I'm having some problems
with
sorting a data frame by the number of occurences of each level of a factor.

df<-data.frame(id=c(1:20),name=c('a','b','b','c','a','d','b','e','d','d','c','a','b','a','a','b','f','b','c','g'))

I want to sort the dataframe so that the values of df$name that occur most
often are at the bottom - ie. in the order:

attributes(sort(summary(df$name)))$name = "e" "f"
"g" "c" "d" "a" "b":
> sort(summary(df$name))
e f g c d a b 
1 1 1 3 3 5 6 

So the desired result is:

id name
8    e
17    f
20    g
 4    c
11    c
19    c
 6    d
 9    d
10    d
  1    a
  5    a
12    a
14    a
15    a
  2    b
  3    b
  7    b
13    b
16    b
18    b


Any suggestions would be greatly appreciated.

Thanks.
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On Fri, Apr 29, 2011 at 11:17:58PM -0700, adigs wrote:
> Apologies for what's probably quite simple, but I'm having some
problems with
> sorting a data frame by the number of occurences of each level of a factor.
> 
>
df<-data.frame(id=c(1:20),name=c('a','b','b','c','a','d','b','e','d','d','c','a','b','a','a','b','f','b','c','g'))
> 
> I want to sort the dataframe so that the values of df$name that occur most
> often are at the bottom - ie. in the order:
> 
> attributes(sort(summary(df$name)))$name = "e" "f"
"g" "c" "d" "a" "b":
> 
> > sort(summary(df$name))
> e f g c d a b 
> 1 1 1 3 3 5 6 
> 
> So the desired result is:
> 
> id name
> 8    e
> 17    f
> 20    g
>  4    c
> 11    c
> 19    c
>  6    d
>  9    d
> 10    d
>   1    a
>   5    a
> 12    a
> 14    a
> 15    a
>   2    b
>   3    b
>   7    b
> 13    b
> 16    b
> 18    b
Hi.

Try the following

  freq <- ave(rep(1, times=nrow(df)), df$name, FUN=sum)
  df[order(freq, df$name), ]

Hope this helps.

Petr Savicky.