Hi Mario,
does acast from the reshape2 package help?
dfa<- data.frame(iso_o = letters[c(1, 1:4)], iso_d = letters[6:10], year =
c(1985, 1985, 1986, 1987, 1988), flow = c(1,2,3,4, NA))
reshape2::acast(dfa, iso_o ~ iso_d, fun.aggregate = sum, value.var = "flow")
HTH
Ulrik
On Fri, 26 May 2017 at 13:47 A M Lavezzi <mario.lave...@unipa.it> wrote:
> Dear R-Users
>
> I have data on bilateral trade flows among countries in the following form:
>
> > head(dataTrade)
>
> 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
>
> where:
> iso_o: code of country of origin
> iso_d: code of country of destination
> year: 1985:2015
> FLOW: amount of trade (values are "NA", 0s, or positive numbers)
>
> 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 such as:
>
> for (i in my_iso){
> for(j in my_iso)
> if(i!=j){
> M[seq(1:length(my_iso))[my_iso==i],seq(1:length(my_iso))[my_iso==j]]
> <-
> sum(dataTrade[dataTrade$iso_o==i &
> dataTrade$iso_d==j,"FLOW"],na.rm=TRUE)
> }
> }
>
> However, it takes ages.
>
> Is there a way to avoid these loops?
>
> Thanks for your help
> Mario
>
>
> --
> Andrea Mario Lavezzi
> DiGi,Sezione Diritto e Società
> Università di Palermo
> Piazza Bologni 8
> 90134 Palermo, Italy
> tel. ++39 091 23892208 <+39%20091%202389%202208>
> fax ++39 091 6111268 <+39%20091%20611%201268>
> skype: lavezzimario
> email: mario.lavezzi (at) unipa.it
> web: http://www.unipa.it/~mario.lavezzi
>
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>
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