[R] Obtaining midpoints of class intervals produced by cut and table

[baptiste auguie]

Hi,

Maybe something like this (inspired by ?cut),

cut2num <- function(f){
  labs <- levels(f)
  d <- data.frame(lower = as.numeric( sub("\\((.+),.*", "\\1", labs) ),
                  upper = as.numeric( sub("[^,]*,([^]]*)\\]", "\\1", labs) ))
  d$midpoints <- rowMeans(d)
  d
}

a <- c(1, 2, 3, 4, 5, 2, 3, 4, 5, 6, 7)
cut2num(cut(a, 3))

HTH,

baptiste





2009/11/8 jose romero <jlaurentum at yahoo.com>:
> Hello list:
>
> I am using "cut" and "table" to obtain a frequency table from a numeric sample vector.  The idea is to calculate mean and standard deviation on grouped data.  However, I can't extract the midpoints of the class intervals, which seem to be strings treated as factors.  How do i extract the midpoint?
>
> Thanks,
> jose loreto
>
>
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