[datatable-help] Fail to add new columns within a function

[Huashan Chen]

OK, here is the complete code with some mock functions from my example.

# data: data.table object
# fn: a filename to read data from 
merge_data<-function(fn, data){
  fs<-getSavedata(fn) # read as data.frame
  if (is.null(fs)) stop('Empty data file')
  
  # return a character vector of variable names which are to merged, some
variables in fs will not be merged to DT
  newvars<-selectVars(names(fs)) 
  stopifnot(length(newvars) > 0)
    
    # determine which rows to use  
    caseid<-someCustomFunc(fs)
  
  add_var<-function(varname){
      data[caseid, `:=`(eval(substitute(varname)), fs[,
toupper(eval(substitute(varname)))]), with=F]  
    }
    invisible(sapply(newvars, add_var))
}

# calling function
merge_data('some file', DT)
DT # display the updated results


In this case, I think a warning from merge_data() when the quota is reached
would be appreciated. Of couse, I could have added a check within the
function to avoid unintended action.

    if (truelength(data) <= ncol(data) + 64L) stop('increase colunmn quota
using alloc.col() before calling this function.')





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