# [R] organizing data in a matrix avoiding loop

A M Lavezzi mario.lavezzi at unipa.it
Fri May 26 18:41:20 CEST 2017

```Hi Duncan
thanks a lot for your suggestion. I followed the suggestion of Sarah (the
first on the thread) and solved my problem

I will keep into account you suggestion anyway
Mario

On Fri, May 26, 2017 at 2:20 PM, Duncan Murdoch <murdoch.duncan at gmail.com>
wrote:

> On 26/05/2017 7:46 AM, A M Lavezzi wrote:
>
>> Dear R-Users
>>
>> 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
>>
>> 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]]
>> <-
>>     }
>> }
>>
>> However, it takes ages.
>>
>> Is there a way to avoid these loops?
>>
>
> Assuming that you have unique entries for each of the first 3 columns, you
> could so something like this:
>
> # Put all the data into an array, indexed by origin, destination, year:
>
> dataMatrix <- as.matrix(dataTrade)  # Converts everything to character
>
> dataArray <- array(0, c(215, 215, 31))
> dimnames(dataArray) <- list(unique(dataMatrix[,1]),
> unique(dataMatrix[,2]), unique(dataMatrix[,3]))
>
>
> # Sum across years
>
> apply(dataArray, 3, sum)
>
> I haven't tried this (you didn't give a reproducible example...), so you
> may need to tweak it a bit.
>
> Duncan Murdoch
>

--
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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