I'm sure I'm doing something wrong, but I'm seeing strange behaviour using the
`head` and `tail` functions on an empty data.frame.
To reproduce:
# create an empty data frame. I actually read an empty table from Excel using
`readWorkbook` from package `openxlsx`
test <- structure(list(Code = NULL, Name = NULL, Address = NULL, Sun.Hrs =
NULL,
Mon.Hrs = NULL), .Names = c("Code", "Name", "Address", "Sun.Hrs",
"Mon.Hrs"), class = "data.frame", row.names = integer(0))
# show the data frame
test
# output in console:
# [1] Code Name Address Sun.Hrs Mon.Hrs
# <0 rows> (or 0-length row.names)
# note that the data frame has 0 rows and 5 columns
# show the structure
str(test)
# output in console:
#'data.frame': 0 obs. of 5 variables:
# $ Code : NULL
# $ Name : NULL
# $ Address: NULL
# $ Sun.Hrs: NULL
# $ Mon.Hrs: NULL
#again, the structure shows 5 columns. However...
head(test); tail(test)
# output in console:
#[1] Name Sun.Hrs
#<0 rows> (or 0-length row.names)
#[1] Name Sun.Hrs
#<0 rows> (or 0-length row.names)
# now we have only two columns
Weird, right?
So, here's my session info:
> sessionInfo()
R version 3.3.1 (2016-06-21)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows >= 8 x64 (build 9200)
locale:
[1] LC_COLLATE=English_United States.1252 LC_CTYPE=English_United States.1252
LC_MONETARY=English_United States.1252 LC_NUMERIC=C
[5] LC_TIME=English_United States.1252
attached base packages:
[1] stats4 grid stats graphics grDevices utils datasets
methods base
other attached packages:
[1] tidyr_0.6.0 lpSolve_5.6.13 flexclust_1.3-4 modeltools_0.2-21
lattice_0.20-34 gtools_3.5.0 reshape2_1.4.1 ash_1.0-15
RODBC_1.3-13
[10] ggmap_2.6.1 ggplot2_2.1.0 dplyr_0.5.0 assertthat_0.1
openxlsx_3.0.0
loaded via a namespace (and not attached):
[1] Rcpp_0.12.7 plyr_1.8.4 tools_3.3.1 digest_0.6.10
tibble_1.2 gtable_0.2.0 png_0.1-7 DBI_0.5-1
mapproj_1.2-4
[10] parallel_3.3.1 proto_0.3-10 stringr_1.1.0 RgoogleMaps_1.4.1
maps_3.1.1 R6_2.1.3 jpeg_0.1-8 sp_1.2-3
magrittr_1.5
[19] scales_0.4.0 geosphere_1.5-5 colorspace_1.2-6 labeling_0.3
stringi_1.1.1 lazyeval_0.2.0 munsell_0.4.3 rjson_0.2.15
This is not an urgent issue, I just think it's curious, so it would be nice to
understand why it happens.
Thanks,
Colin
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