How about? Trade <- xtabs(FLOW ~ iso_o + iso_d + year, dta)
Gives you a 3d table with FLOW as the cell entry. Then apply(Trade, 1:2, sum, na.rm=TRUE) Gives you a 2d table with the total flow David L. Carlson Department of Anthropology Texas A&M University -----Original Message----- From: R-help [mailto:r-help-boun...@r-project.org] On Behalf Of S Ellison Sent: Friday, May 26, 2017 8:28 AM To: A M Lavezzi <mario.lave...@unipa.it>; r-help <r-help@r-project.org> Subject: Re: [R] organizing data in a matrix avoiding loop > -----Original Message----- > From: A M > Lavezzi > > I have data on bilateral trade flows among countries in the following form: > > iso_o iso_d year FLOW > 1 ABW AFG 1985 NA > 2 ABW AFG 1986 NA > 3 ABW AFG 1987 NA > 4 ABW AFG 1988 NA > 5 ABW AFG 1989 NA > 6 ABW AFG 1990 NA > >... > > I have 215 countries. I would like to create a 215x215 matrix , say M, in > which > element M(i,j) is the total trade between countries i and j between > 1985 and 2015 (i.e. the sum of annual amounts of trade). > > After collecting the country codes in a variable named "my_iso", I can obtain > M in a straightforward way using a loop > > Is there a way to avoid these loops? Using core R: #Use aggregate() to aggregate across years: dataTrade.ag <- aggregate (dataTrade[,'Flow',drop=FALSE], by=dataTrade[, c('iso_o', 'iso_d')], FUN=sum, na.rm=TRUE) #where na.rm=TRUE (passed to sum()) essentially treats NAs as 0. If you really want NA leave it out or set it to FALSE #This gives you one row per origin/destination pair that contains the total trade in Flow. #If the years you want are a subset, subset the data frame first. #Form an empty matrix with suitable dimnames: N_iso <- length(my_iso) dT.m <- matrix(rep(NA, N_iso*N_iso), ncol=N_iso, dimnames=list(my_iso, my_iso)) #Then use matrix indexing by name to populate your matrix with the available flow data dT.m[as.matrix(dataTrade.ag[1:2]) ] <- dataTrade.ag$Flow #This relies on a default conversion from data frame factors to a character matrix, together #with R's facility for matrix indexing by 2-column matrix #Then dataTrade.ag[1:10, 1:10] #should have what you seem to want S Ellison ******************************************************************* This email and any attachments are confidential. Any use...{{dropped:14}} ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.
