Provide aggregation support for rank histogram line type RHIST

[bikegeek]

Describe the Enhancement

The RHIST line type from the MET tool ensemble-stat requires support for aggregating, by following the logic in the original R script:

For ranked histogram, it looks like after the optional event equalization is performed, the sum is calculated in this code:
(line 103 rhist.R_tmpl)

#calculate sum
sum_by = list(i_value=dfData$i_value);
columns = c("i_value")
for(seriesVal in names(listSeries1Val)){
  sum_by[seriesVal]=dfData[seriesVal]
  columns = c(columns, seriesVal)
}
columns = c(columns, "stat_value")
dfData=setNames(aggregate(x=dfData$rank_i, by=sum_by, FUN=sum), columns)

found in the METviewer repository:
https://github.com/dtcenter/METviewer/blob/main_v5.1/R_tmpl/rhist.R_tmpl

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