In the introduction of Computational Actuarial Science with R, there was a short paragraph on how could we import only some parts of a large database, by selecting specific variables. The trick was to use the following
> read.table.select.columns=function(datatablename, I,sep=";"){ + datanc=read.table(datatablename,header=TRUE, sep=sep,skip=0,nrows=1) + mycols=rep("NULL",ncol(datanc)) + names(mycols)=names(datanc) + mycols[I]=NA + datat=read.table(datatablename,header=TRUE, sep=sep,colClasses=mycols) + return(datat)}
For instance, if we use the same dataset as in the introduction, we can import only two variables of interest,
> loc="http://myweb.fsu.edu/jelsner/extspace/extremedatasince1899.csv" > dt1=read.table.select.columns(loc,c("Region", "Wmax"),sep=",") > head(dt1,10) Region Wmax 1 Basin 105.56342 2 Basin 40.00000 3 Basin 35.41822 4 Basin 51.06743 5 Florida 87.34328 6 Basin 96.64138 7 Gulf 35.41822 8 US 35.41822 9 US 87.34328 10 US 106.35318 > dim(dt1) [1] 2100 2
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