Hey Everyone!
I´m a quite new R user .. I found a problem that I'd like to share with you
and help me find a solution.
I have a large txt. file which I opened with read.table command, and what I
understood from many R manuals is that I have a kind of matrix readed with
read.table,
I've used order() to sort my data and now my problem is: I have a variable
that has many repeated values and I would like to operate with the row
indexes of "these repeated values": for example, suppose I have:
var1 var2
varN
122 nnn1
1
213 nnn2
2
422 nnn4
2
432
3
441
4
500
4
550
4
So I want to obtain a new column where all elements of var1 are added at the
places where varN are repetead ... so for varN=2 the new column correspond
to this element will be 213+422, for varN=4 will be 441+500+550, where there
is no such repeated values obviously there´s nothing to do and varN is the
unique value.
I made a function to do this but is not so good, (I hava a database with
around 1 million rows and 5 columns) actually, this function works for not
so large data:
suma.rep=function(X,Y){
resp=numeric(0)
Z=unique(Y)
for (i in (1:length(Z)))
resp=c(resp,sum(X[which(Y==Z[i])]))
return(resp)}
When I run this function with my large data, R appears calculating and I
think it would take so long to make my new required column.(maybe 4 days)
Question1: I "feel" that maybe there's a command that could help me to do
this "simple" operation more elegant, I googled it but I couldnt find... Is
there any such a command?
Question2: Is a good idea to handle large data bases files with R, as in my
example?
Thank you so much for your help.
Christian Paúl
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