[R] organizing data in a matrix avoiding loop

[Sarah Goslee]

There are various ways to do this. It shouldn't take forever as a loop,
with only 215 entries.

I find crosstab() from the ecodist package helpful. The current version is
on GitHub, but not yet CRAN (soon!).

Sarah

On Fri, May 26, 2017 at 7:47 AM A M Lavezzi <mario.lavezzi at 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
> fax ++39 091 6111268
> skype: lavezzimario
> email: mario.lavezzi (at) unipa.it
> web: http://www.unipa.it/~mario.lavezzi
>
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>
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-- 
Sarah Goslee
http://www.stringpage.com
http://www.sarahgoslee.com
http://www.functionaldiversity.org

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