[R] Using a 'for' loop : there should be a better way in R

[John Kane]

--- Gabor Grothendieck <ggrothendieck at gmail.com>
wrote:

> Use cbind to create a two column matrix, mat,
> and multiply that by the appropriate inflation
> factors.
> Then use rowsum to sum the rows according to the
> id grouping factor.
> 
> inf.fac <- list(year1 = 1, year2 = 5, year3 = 10)
> mat <- cbind(s1 = df1$cat1 + df1$cat2, s2 = df1$cat3
> + df1$cat4)
> rowsum(mat * unlist(inf.fac[df1$year]), df1$id)

Thanks very much.  It took me a few minutes to see
what was happening but it is lovely.  I would never
have thought of using a list like that.
> 
> 
> On 8/24/06, John Kane <jrkrideau at yahoo.ca> wrote:
> > I need to apply a yearly inflation factor to some
> > wages and supply some simple sums by work
> category.  I
> > have gone at it with a brute force "for" loop
> approach
> >  which seems okay as it is a small dataset.  It
> looks
> > a bit inelegant and given all the warnings in the
> > Intro to R, etc, about using loops I wondered  if
> > anyone could suggest something a bit simpler or
> more
> > efficent?
> >
> > Example:
> >
> > cat1 <- c( 1,1,6,1,1,5)
> > cat2 <- c( 1,2,3,4,5,6)
> > cat3 <- c( 5,4,6,7,8,8)
> > cat4 <- c( 1,2,1,2,1,2)
> > years <- c( 'year1', 'year2', 'year3', 'year3',
> > 'year1', 'year1')
> > id <-  c('a','a','b','c','c','a')
> > df1 <- data.frame(id,years,cat1,cat2, cat3, cat4)
> >
> > nn <- levels(df1$id)    # levels for outer loop
> > hh <- levels(df1$years) # levels for inter loop
> >
> >
> > mp <- c(1, 5, 10)   # inflation factor
> >
> > tt <- data.frame(matrix(NA, length(nn), 2))
> > names(tt) <- c("s1","s2")
> > rownames(tt) <- nn
> >
> > for (i in 1:length(nn)){
> > scat <- data.frame(matrix(NA, length(hh),2))
> > dd1 <- subset(df1, id==nn[i])
> > for (j in 1:length(hh)){
> > dd2 <- subset(dd1, dd1$years==hh[j])
> > s1 <- sum(dd2$cat1,dd2$cat2, na.rm=T)
> > s2 <- sum(dd2$cat3,dd2$cat4,na.rm=T)
> > scat[j,] <- c(s1,s2) *mp[j]    # multiply by the
> > inflation factor
> > }
> > crush <- apply(scat, 2, sum)
> > tt[i,] <- crush
> > }
> > tt
> >
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> > PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained,
> reproducible code.
> >
>