[R] organizing data in a matrix avoiding loop

[A M Lavezzi]

Hi David
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 4:51 PM, David L Carlson <dcarlson at tamu.edu> wrote:

> 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-bounces at r-project.org] On Behalf Of S Ellison
> Sent: Friday, May 26, 2017 8:28 AM
> To: A M Lavezzi <mario.lavezzi at unipa.it>; r-help <r-help at 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:
>
> https://urlsand.esvalabs.com/?u=http%3A%2F%2FdataTrade.ag&e=
> ae0ec65b&h=cb58f304&f=y <- 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
>
>
>
>
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-- 
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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