[R] count the # of appearances...

[Stephen Tucker]

You can split() the original vector according to its elements into a list,
then use lapply() to count the lengths of the list:

> x <- round(runif(100,1,10))
> unlist(lapply(split(x,f=x),length))
 1  2  3  4  5  6  7  8  9 10 
 5 14  9 13 11  8  8 14 12  6 

This can be useful if you want to use some criteria for counting, and then
you can replace length() with your own function.

Best regards,

ST


--- ted.harding at nessie.mcc.ac.uk wrote:

> On 01-Mar-07 bunny , lautloscrew.com wrote:
> > Hi there,
> > 
> > is there a possibility to count the number of appearances of an  
> > element in a vector ?
> > i mean of any given element.. deliver all elements which are exactly  
> > xtimes in this vector ?
> > 
> > thx in advance !!
> 
> If it is a specific element value which you designate beforehand,
> then Ranjan Maitra's method
> 
>   sum(your vector == your chosen element)
> 
> will of course give you the number of times this occurs.
> 
> However, your query suggests this may not be what you want.
> 
> First, if you do not designate a specific element, then table()
> can give you counts of repetitions of all the distinct elements.
> For example:
> 
> ## Generate the vector y with repetitions of elements of x:
> > x<-round(runif(10),digits=3)
> > y<-sample(x,25,replace=TRUE)
> 
> ## Count the numbers of repetitions
> > x<-round(runif(10),digits=3)
> > y<-sample(x,25,replace=TRUE)
> > table(y)
> ## y
> ## 0.122 0.372 0.431 0.486 0.523 0.858 0.886 0.948 
> ##    5     4     5     3     3     2     2     1 
> 
> Second: You ask for a method to "deliver all elements which are
> exactly xtimes in this vector". So suppose "xtimes" is a given
> number of times, and you want to know all elements which each
> occur xtimes times in the vector y.
> 
> You could base a method for this on the ouput of table()
> as above (look at "?table" for the background).
> 
>   counts <- as.data.frame(table(y))
>   counts
> ##       y Freq
> ## 1 0.122    5
> ## 2 0.372    4
> ## 3 0.431    5
> ## 4 0.486    3
> ## 5 0.523    3
> ## 6 0.858    2
> ## 7 0.886    2
> ## 8 0.948    1
> 
> so, if your "xtimes" is say 3, then
> 
>   counts$y[counts$Freq==3]
> ## [1] 0.486 0.523
> ## Levels: 0.122 0.372 0.431 0.486 0.523 0.858 0.886 0.948
> 
> showing that elements "0.486" and "0.523" occurred 3 times each
> in the vector y.
> 
> Hoping this helps,
> Ted.
> 
> --------------------------------------------------------------------
> E-Mail: (Ted Harding) <ted.harding at nessie.mcc.ac.uk>
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> Date: 01-Mar-07                                       Time: 15:11:09
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