[R] How to convert category (or range/group) into continuous?

[Leonard Mada]

Dear Marna,


If you want to extract the middle of those intervals, please find below 
an improved variant of Luigi's code.


Note:
- it is more efficient to process the levels of a factor, instead of all 
the individual strings;
- I envision that there are benefits in a large data frame (> 1 million 
rows) - although I have not explicitly checked it;
- the code also handles better the open/closed intervals;
- the returned data structure may require some tweaking (currently 
returns a data.frame);



### Middle of an Interval
mid.factor = function(x, inf.to = NULL, split.str=",") {
     lvl0 = levels(x); lvl = lvl0;
     lvl = sub("^[(\\[]", "", lvl);
     lvl = sub("[])]$", "", lvl); # tricky;
     lvl = strsplit(lvl, split.str);
     lvl = lapply(lvl, function(x) as.numeric(x));
     if( ! is.null(inf.to)) {
         FUN = function(x) {
             if(any(x == Inf)) 1
             else if(any(x == - Inf)) -1
             else 0;
         }
         whatInf = sapply(lvl, FUN);
         # TODO: more advanced;
         lvl[whatInf == -1] = inf.to[1];
         lvl[whatInf ==  1] = inf.to[2];
     }
     mid = sapply(lvl, mean);
     lvl = data.frame(lvl=lvl0, mid=mid);
     merge(data.frame(lvl=x), lvl, by="lvl");
}


# uses the daT data frame;
# requires a factor:
# - this is probably the case with the original data;
daT$group = as.factor(daT$group);
mid.factor(daT$group);


I have uploaded this code also on my GitHub list of useful data tools:

https://github.com/discoleo/R/blob/master/Stat/Tools.Data.R


Sincerely,


Leonard