Month: April 2015

Reading fixed width formats in the Hadleyverse

This is an update to a previous post on reading fixed width formats in R.

A new addition to the Hadleyverse is the package readr, which includes a function read_fwf to read fixed width format files. I’ll compare the LaF approach to the readr approach using the same dataset as before. The variable wt is generated from parsing the Stata load file as before.

I want to read all the data in two columns: DRG and HOSPID. The LaF solution for this is:

d <- laf_open_fwf('NIS_2008_Core.ASC', column_widths=wt$widths,
                  column_types=wt$classes, column_names = wt$varnames)
d1 <- d[,c('DRG','HOSPID')]

For readr, we use the following code:

x <-$widths, wt$varnames))
fwfpos <- fwf_positions(x[c(15,62),1], x[c(15,62),2], col_names=c(x[c(15,62),3]))
d1 <- read_fwf('NIS_2008_Core.ASC', fwfpos)

As a comparison of times on my MacBook Air (2014) with 8GB memory and a 1.4 GHz Intel Core i5 and a Solid State Disk, the LaF approach took 20.73s (system time 2.52s), while the readr solution takes 40.23s (system time 10.55s). While readr has improved things a lot compared to read.fwf and other base R solutions, the LaF approach is still more efficient.