According to ?fread:
nrows=0 returns the column names and typed empty columns determined by the large sample
But this is not true if an integer 0L is passed:
f <- tempfile(fileext = ".csv")
fwrite(mtcars, f)
fread(f, nrows = 0)
# Empty data.table (0 rows and 11 cols): mpg,cyl,disp,hp,drat,wt...
fread(f, nrows = 0L)
# mpg cyl disp hp drat wt qsec vs am gear carb
# <num> <int> <num> <int> <num> <num> <num> <int> <int> <int> <int>
# 1: 21.0 6 160.0 110 3.90 2.620 16.46 0 1 4 4
# 2: 21.0 6 160.0 110 3.90 2.875 17.02 0 1 4 4
# 3: 22.8 4 108.0 93 3.85 2.320 18.61 1 1 4 1
# 4: 21.4 6 258.0 110 3.08 3.215 19.44 1 0 3 1
# 5: 18.7 8 360.0 175 3.15 3.440 17.02 0 0 3 2
# 6: 18.1 6 225.0 105 2.76 3.460 20.22 1 0 3 1
# 7: 14.3 8 360.0 245 3.21 3.570 15.84 0 0 3 4
# 8: 24.4 4 146.7 62 3.69 3.190 20.00 1 0 4 2
# 9: 22.8 4 140.8 95 3.92 3.150 22.90 1 0 4 2
# 10: 19.2 6 167.6 123 3.92 3.440 18.30 1 0 4 4
# 11: 17.8 6 167.6 123 3.92 3.440 18.90 1 0 4 4
# 12: 16.4 8 275.8 180 3.07 4.070 17.40 0 0 3 3
# 13: 17.3 8 275.8 180 3.07 3.730 17.60 0 0 3 3
# 14: 15.2 8 275.8 180 3.07 3.780 18.00 0 0 3 3
# 15: 10.4 8 472.0 205 2.93 5.250 17.98 0 0 3 4
# 16: 10.4 8 460.0 215 3.00 5.424 17.82 0 0 3 4
# 17: 14.7 8 440.0 230 3.23 5.345 17.42 0 0 3 4
# 18: 32.4 4 78.7 66 4.08 2.200 19.47 1 1 4 1
# 19: 30.4 4 75.7 52 4.93 1.615 18.52 1 1 4 2
# 20: 33.9 4 71.1 65 4.22 1.835 19.90 1 1 4 1
# 21: 21.5 4 120.1 97 3.70 2.465 20.01 1 0 3 1
# 22: 15.5 8 318.0 150 2.76 3.520 16.87 0 0 3 2
# 23: 15.2 8 304.0 150 3.15 3.435 17.30 0 0 3 2
# 24: 13.3 8 350.0 245 3.73 3.840 15.41 0 0 3 4
# 25: 19.2 8 400.0 175 3.08 3.845 17.05 0 0 3 2
# 26: 27.3 4 79.0 66 4.08 1.935 18.90 1 1 4 1
# 27: 26.0 4 120.3 91 4.43 2.140 16.70 0 1 5 2
# 28: 30.4 4 95.1 113 3.77 1.513 16.90 1 1 5 2
# 29: 15.8 8 351.0 264 4.22 3.170 14.50 0 1 5 4
# 30: 19.7 6 145.0 175 3.62 2.770 15.50 0 1 5 6
# 31: 15.0 8 301.0 335 3.54 3.570 14.60 0 1 5 8
# 32: 21.4 4 121.0 109 4.11 2.780 18.60 1 1 4 2
# mpg cyl disp hp drat wt qsec vs am gear carb
Output of sessionInfo()
# R version 3.6.2 (2019-12-12)
# Platform: x86_64-pc-linux-gnu (64-bit)
# Running under: Arch Linux
#
# Matrix products: default
# BLAS: /usr/lib/libblas.so.3.9.0
# LAPACK: /usr/lib/liblapack.so.3.9.0
#
# locale:
# [1] LC_CTYPE=en_US.UTF-8 LC_NUMERIC=C
# [3] LC_TIME=en_US.UTF-8 LC_COLLATE=en_US.UTF-8
# [5] LC_MONETARY=en_US.UTF-8 LC_MESSAGES=en_US.UTF-8
# [7] LC_PAPER=en_US.UTF-8 LC_NAME=C
# [9] LC_ADDRESS=C LC_TELEPHONE=C
# [11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C
#
# attached base packages:
# [1] stats graphics grDevices utils datasets methods base
#
# other attached packages:
# [1] eplusr_0.12.0.9000 testthat_2.3.2 nvimcom_0.9-98
#
# loaded via a namespace (and not attached):
# [1] progress_1.2.2 xfun_0.16
# [3] remotes_2.2.0 vctrs_0.3.2
# [5] generics_0.0.2 miniUI_0.1.1.1
# [7] usethis_1.5.1.9000 htmltools_0.5.0
# [9] blob_1.2.1 rlang_0.4.7
# [11] pkgbuild_1.1.0 manipulateWidget_0.10.0
# [13] later_1.0.0 glue_1.4.1
# [15] withr_2.2.0 DBI_1.1.0
# [17] bit64_0.9-7 sessioninfo_1.1.1
# [19] devtools_2.2.2 htmlwidgets_1.5.1
# [21] memoise_1.1.0 knitr_1.29
# [23] callr_3.4.3 fastmap_1.0.1
# [25] httpuv_1.5.2 ps_1.3.4
# [27] crosstalk_1.0.0 parallel_3.6.2
# [29] fansi_0.4.1 Rcpp_1.0.5
# [31] xtable_1.8-4 backports_1.1.8
# [33] promises_1.1.0 checkmate_2.0.0
# [35] desc_1.2.0 pkgload_1.1.0
# [37] webshot_0.5.2 jsonlite_1.7.0
# [39] mime_0.9 fs_1.4.2
# [41] bit_1.1-15.2 hms_0.5.3
# [43] digest_0.6.25 stringi_1.4.6
# [45] processx_3.4.3 shiny_1.4.0
# [47] rprojroot_1.3-2 cli_2.0.2
# [49] tools_3.6.2 magrittr_1.5
# [51] rgl_0.100.30 RSQLite_2.2.0
# [53] crayon_1.3.4 pkgconfig_2.0.3
# [55] ellipsis_0.3.1 data.table_1.12.4
# [57] prettyunits_1.1.1 decido_0.2.0
# [59] lubridate_1.7.8 assertthat_0.2.1
# [61] rstudioapi_0.11 R6_2.4.1
# [63] units_0.6-6 compiler_3.6.2
According to
?fread:But this is not true if an integer
0Lis passed:Output of
sessionInfo()