Aggregate variables in list of data frames into single data frame

Question

I am performing a per policy life insurance valuation in R. Monthly cash flow projections are performed per policy and returns a data frame in the following format (for exam

Answer 1

I think this solution might be efficient. Give it a try and let me know

require(data.table)
newagg <- function(dataset) { dataset <- data.table(dataset);dataset <- dataset[,lapply(.SD,sum),by=ProjM,.SDcols=c("Cashflow1","Cashflow2")]; return(dataset)}
newagg(rbindlist(lapply(ListOfDataFrames,newagg)))
# ProjM Cashflow1 Cashflow2
# 1:     1        55       -35
# 2:     2        55       -35
# 3:     3        55       -35
# 4:     4         5        10
# 5:     5         5        10