When I read a CSV file containing a trailing delimiter using readr::read_csv(), I get a warning that a new name for the last column was created. Here is the contents of a short example file to show what a mean:
A,B,C,
2,1,1,
14,22,5,
9,-4,8,
17,9,-3,
Note the trailing comma at the end of each row. Now if I load this data with
readr::read_csv("A,B,C,\n2,1,1,\n14,22,5,\n9,-4,8,\n17,9,-3,")
I get the following message:
New names:
• `` -> `...4`
The resulting tibble has an extra fourth column names ...4 consisting of NA values in each row:
# A tibble: 4 × 4
A B C ...4
<dbl> <dbl> <dbl> <lgl>
1 2 1 1 NA
2 14 22 5 NA
3 9 -4 8 NA
4 17 9 -3 NA
Even if I explicitly load only the first three columns with
read_csv(
"A,B,C,\n2,1,1,\n14,22,5,\n9,-4,8,\n17,9,-3,",
col_types=cols_only(
A=col_integer(),
B=col_integer(),
C=col_integer()
)
)
I still get this message.
Is this the expected behavior or is there some way to tell readr::read_csv() that it is supposed to ignore all columns except the ones I specify? Or is there another way to tidy up this (apparently malformed) CSV so that trailing delimiters are deleted/ignored?
I don't think you can. From what I can see in the documentation, cols_only() is for R objects that you have already loaded in.
However, the fread() function from the data.table library allows you to select specific column names as a file is read in:
DT <- fread("filename.csv", select = c("colA","colB"))