Using cut2 from Hmisc to calculate cuts for different number of groups

r quantile hmisc
lucyh picture lucyh · May 3, 2013 · Viewed 9.5k times · Source

I was trying to calculate equal quantile cuts for a vector by using cut2 from Hmisc. 

library(Hmisc)
c <- c(-4.18304,-3.18343,-2.93237,-2.82836,-2.13478,-2.01892,-1.88773,
       -1.83124,-1.74953,-1.74858,-0.63265,-0.59626,-0.5681)

cut2(c, g=3, onlycuts=TRUE)

[1] -4.18304 -2.01892 -1.74858 -0.56810

But I was expecting the following result (33%, 33%, 33%):

[1] -4.18304 -2.13478 -1.74858 -0.56810

Should I still use cut2 or try something different? How can I make it work? Thanks for your advice.

Answer

IRTFM picture IRTFM · May 3, 2013

You are seeing the cutpoints, but you want the tabular counts, and you want them as fractions of the total, so do this instead:

> prop.table(table(cut2(c, g=3) ) )

[-4.18,-2.019) [-2.02,-1.749) [-1.75,-0.568] 
     0.3846154      0.3076923      0.3076923

(Obviously you cannot expect cut2 to create an exact split when the count of elements was not evenly divisible by 3.)

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