[R] Using read.csv.sql() to read in specific columns
HDoran at air.org
Thu Sep 18 17:38:18 CEST 2014
I am dealing with data frames that have thousands of columns and hundreds of thousands of rows and only need a few specific columns from the data. The data take various formats, but normally are tab-delimited.
I have written the following which is working as expected. However, because Im so new at using sqldf(), just looking for some verification from users that this is in fact efficient and correct in the R-ish sense of the word and generalizable to larger data sets.
tmp <- data.frame(replicate(50, rnorm(10)))
names(tmp) <- paste('item', 1:50, sep='')
read.csv.sql("tmp.txt", sql = "select item1, item2, item50 from file", sep = ' ')
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