问题
I have a zip archive with several csv files in it. I would like to use fread to import selected csv files into R.
With read.csv I can get the data as follows without extracting the archive.
con <- unz("myarchive.zip", "file2.csv")
file2 <- read.csv(con, header=T, sep=",", stringsAsFactors = FALSE)
on.exit(close(con))
How to use data.table::fread to import the the data in the csv file into R from the archive without extracting it?
回答1:
fread can run shell commands to preprocess the file, so eg on Linux this works:
write.csv(mtcars, 'mtcars.csv')
zip('mtcars.csv.zip', 'mtcars.csv')
# adding: mtcars.csv (deflated 52%)
fread('unzip -cq mtcars.csv.zip')
# V1 mpg cyl disp hp drat wt qsec vs am gear carb
# 1: Mazda RX4 21.0 6 160.0 110 3.90 2.620 16.46 0 1 4 4
# 2: Mazda RX4 Wag 21.0 6 160.0 110 3.90 2.875 17.02 0 1 4 4
# 3: Datsun 710 22.8 4 108.0 93 3.85 2.320 18.61 1 1 4 1
# 4: Hornet 4 Drive 21.4 6 258.0 110 3.08 3.215 19.44 1 0 3 1
# 5: Hornet Sportabout 18.7 8 360.0 175 3.15 3.440 17.02 0 0 3 2
# 6: Valiant 18.1 6 225.0 105 2.76 3.460 20.22 1 0 3 1
# 7: Duster 360 14.3 8 360.0 245 3.21 3.570 15.84 0 0 3 4
# 8: Merc 240D 24.4 4 146.7 62 3.69 3.190 20.00 1 0 4 2
# 9: Merc 230 22.8 4 140.8 95 3.92 3.150 22.90 1 0 4 2
# 10: Merc 280 19.2 6 167.6 123 3.92 3.440 18.30 1 0 4 4
# 11: Merc 280C 17.8 6 167.6 123 3.92 3.440 18.90 1 0 4 4
# 12: Merc 450SE 16.4 8 275.8 180 3.07 4.070 17.40 0 0 3 3
# 13: Merc 450SL 17.3 8 275.8 180 3.07 3.730 17.60 0 0 3 3
# 14: Merc 450SLC 15.2 8 275.8 180 3.07 3.780 18.00 0 0 3 3
# 15: Cadillac Fleetwood 10.4 8 472.0 205 2.93 5.250 17.98 0 0 3 4
# 16: Lincoln Continental 10.4 8 460.0 215 3.00 5.424 17.82 0 0 3 4
# 17: Chrysler Imperial 14.7 8 440.0 230 3.23 5.345 17.42 0 0 3 4
# 18: Fiat 128 32.4 4 78.7 66 4.08 2.200 19.47 1 1 4 1
# 19: Honda Civic 30.4 4 75.7 52 4.93 1.615 18.52 1 1 4 2
# 20: Toyota Corolla 33.9 4 71.1 65 4.22 1.835 19.90 1 1 4 1
# 21: Toyota Corona 21.5 4 120.1 97 3.70 2.465 20.01 1 0 3 1
# 22: Dodge Challenger 15.5 8 318.0 150 2.76 3.520 16.87 0 0 3 2
# 23: AMC Javelin 15.2 8 304.0 150 3.15 3.435 17.30 0 0 3 2
# 24: Camaro Z28 13.3 8 350.0 245 3.73 3.840 15.41 0 0 3 4
# 25: Pontiac Firebird 19.2 8 400.0 175 3.08 3.845 17.05 0 0 3 2
# 26: Fiat X1-9 27.3 4 79.0 66 4.08 1.935 18.90 1 1 4 1
# 27: Porsche 914-2 26.0 4 120.3 91 4.43 2.140 16.70 0 1 5 2
# 28: Lotus Europa 30.4 4 95.1 113 3.77 1.513 16.90 1 1 5 2
# 29: Ford Pantera L 15.8 8 351.0 264 4.22 3.170 14.50 0 1 5 4
# 30: Ferrari Dino 19.7 6 145.0 175 3.62 2.770 15.50 0 1 5 6
# 31: Maserati Bora 15.0 8 301.0 335 3.54 3.570 14.60 0 1 5 8
# 32: Volvo 142E 21.4 4 121.0 109 4.11 2.780 18.60 1 1 4 2
# V1 mpg cyl disp hp drat wt qsec vs am gear carb
来源：https://stackoverflow.com/questions/35644556/using-fread-to-import-csv-file-from-an-archive-into-r-without-extracting-to