mathijsdevaan wrote: > > I have a DF like this: > > DF = data.frame(read.table(textConnection(" A B C > 1 b1 1999 0.25 > 2 c1 1999 0.25 > .. > For each factor in A I want to sum the values of C for all years(Bn) prior > to the current year(Bi): > > 1 b1 1999 0.25 0 > 2 c1 1999 0.25 0.4 > 3 d1 1999 0.25 0 > > In steps following the "thinking order". You could shorten this considerably. I slightly changed you column names to more speakable ones.
Dieter DF = data.frame(read.table(textConnection(" group year C 1 b1 1999 0.25 2 c1 1999 0.25 3 d1 1999 0.25 4 a2 1999 0.25 5 c2 1999 0.25 6 d2 1999 0.25 7 a3 1999 0.25 8 b3 1999 0.25 9 d3 1999 0.25 10 a4 1999 0.25 11 b4 1999 0.25 12 c4 1999 0.25 13 b1 2001 0.5 14 a2 2001 0.5 15 b1 2004 0.33 16 c1 2004 0.33 17 a2 2004 0.33 18 c2 2004 0.33 19 a3 2004 0.33 20 b3 2004 0.33 21 d2 1980 0.4 22 a3 1980 0.4 23 b4 1981 0.4 24 c1 1981 0.4"),head=TRUE)) by(DF,DF$group, FUN = function(x){ print(str(x)) }) # Looks like we should order... # Other solutions are possible, but ordering all first might (not tested) # be the most efficient way for large sets DF = DF[order(DF$group,DF$year),] # Let's try cumsum on each group by(DF,DF$group, FUN = function(x){ cumsum(x$C) }) # That's not exactly your defininition of "prior" # correct for first value by(DF,DF$group, FUN = function(x){ cumsum(x$C)-x$C }) # Now the data are in right order, make vector of result DF$D = unlist(by(DF,DF$group, FUN = function(x){ cumsum(x$C) })) # You could sort by row names now to restore the old order -- View this message in context: http://r.789695.n4.nabble.com/Conditional-sum-tp3315163p3315279.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.