input
A single character string. The value is inspected and deferred to either file=
(if no \n present), text=
(if at least one \n is present) or cmd=
(if no \n is present, at least one space is present, and it isn't a file name). Exactly one of input=
, file=
, text=
, or cmd=
should be used in the same call.
file
File name in working directory, path to file (passed through path.expand
for convenience), or a URL starting http://, file://, etc. Compressed files with extension ‘.gz’ and ‘.bz2’ are supported if the R.utils
package is installed.
text
The input data itself as a character vector of one or more lines, for example as returned by readLines()
.
cmd
A shell command that pre-processes the file; e.g. fread(cmd=paste("grep",word,"filename"))
. See Details.
sep
The separator between columns. Defaults to the character in the set [,\t |;:]
that separates the sample of rows into the most number of lines with the same number of fields. Use NULL
or ""
to specify no separator; i.e. each line a single character column like base::readLines
does.
sep2
The separator within columns. A list
column will be returned where each cell is a vector of values. This is much faster using less working memory than strsplit
afterwards or similar techniques. For each column sep2
can be different and is the first character in the same set above [,\t |;
], other than sep
, that exists inside each field outside quoted regions in the sample. NB: sep2
is not yet implemented.
nrows
The maximum number of rows to read. Unlike read.table
, you do not need to set this to an estimate of the number of rows in the file for better speed because that is already automatically determined by fread
almost instantly using the large sample of lines. nrows=0
returns the column names and typed empty columns determined by the large sample; useful for a dry run of a large file or to quickly check format consistency of a set of files before starting to read any of them.
header
Does the first data line contain column names? Defaults according to whether every non-empty field on the first data line is type character. If so, or TRUE is supplied, any empty column names are given a default name.
na.strings
A character vector of strings which are to be interpreted as NA
values. By default, ",,"
for columns of all types, including type character
is read as NA
for consistency. ,"",
is unambiguous and read as an empty string. To read ,NA,
as NA
, set na.strings="NA"
. To read ,,
as blank string ""
, set na.strings=NULL
. When they occur in the file, the strings in na.strings
should not appear quoted since that is how the string literal ,"NA",
is distinguished from ,NA,
, for example, when na.strings="NA"
.
stringsAsFactors
Convert all character columns to factors?
verbose
Be chatty and report timings?
skip
If 0 (default) start on the first line and from there finds the first row with a consistent number of columns. This automatically avoids irregular header information before the column names row. skip>0
means ignore the first skip
rows manually. skip="string"
searches for "string"
in the file (e.g. a substring of the column names row) and starts on that line (inspired by read.xls in package gdata).
select
A vector of column names or numbers to keep, drop the rest. select
may specify types too in the same way as colClasses
; i.e., a vector of colname=type
pairs, or a list
of type=col(s)
pairs. In all forms of select
, the order that the columns are specified determines the order of the columns in the result.
drop
Vector of column names or numbers to drop, keep the rest.
colClasses
As in utils::read.csv
; i.e., an unnamed vector of types corresponding to the columns in the file, or a named vector specifying types for a subset of the columns by name. The default, NULL
means types are inferred from the data in the file. Further, data.table
supports a named list
of vectors of column names or numbers where the list
names are the class names; see examples. The list
form makes it easier to set a batch of columns to be a particular class. When column numbers are used in the list
form, they refer to the column number in the file not the column number after select
or drop
has been applied.
If type coercion results in an error, introduces NA
s, or would result in loss of accuracy, the coercion attempt is aborted for that column with warning and the column's type is left unchanged. If you really desire data loss (e.g. reading 3.14
as integer
) you have to truncate such columns afterwards yourself explicitly so that this is clear to future readers of your code.
integer64
"integer64" (default) reads columns detected as containing integers larger than 2^31 as type bit64::integer64
. Alternatively, "double"|"numeric"
reads as utils::read.csv
does; i.e., possibly with loss of precision and if so silently. Or, "character".
dec
The decimal separator as in utils::read.csv
. If not "." (default) then usually ",". See details.
col.names
A vector of optional names for the variables (columns). The default is to use the header column if present or detected, or if not "V" followed by the column number. This is applied after check.names
and before key
and index
.
check.names
default is FALSE
. If TRUE
then the names of the variables in the data.table
are checked to ensure that they are syntactically valid variable names. If necessary they are adjusted (by make.names
) so that they are, and also to ensure that there are no duplicates.
encoding
default is "unknown"
. Other possible options are "UTF-8"
and "Latin-1"
. Note: it is not used to re-encode the input, rather enables handling of encoded strings in their native encoding.
quote
By default ("\""
), if a field starts with a double quote, fread
handles embedded quotes robustly as explained under Details
. If it fails, then another attempt is made to read the field as is, i.e., as if quotes are disabled. By setting quote=""
, the field is always read as if quotes are disabled. It is not expected to ever need to pass anything other than \"\" to quote; i.e., to turn it off.
strip.white
default is TRUE
. Strips leading and trailing whitespaces of unquoted fields. If FALSE
, only header trailing spaces are removed.
fill
logical (default is FALSE
). If TRUE
then in case the rows have unequal length, blank fields are implicitly filled.
blank.lines.skip
logical
, default is FALSE
. If TRUE
blank lines in the input are ignored.
key
Character vector of one or more column names which is passed to setkey
. It may be a single comma separated string such as key="x,y,z"
, or a vector of names such as key=c("x","y","z")
. Only valid when argument data.table=TRUE
. Where applicable, this should refer to column names given in col.names
.
index
Character vector or list of character vectors of one or more column names which is passed to setindexv
. As with key
, comma-separated notation like index="x,y,z"
is accepted for convenience. Only valid when argument data.table=TRUE
. Where applicable, this should refer to column names given in col.names
.
showProgress
-
TRUE
displays progress on the console if the ETA is greater than 3 seconds. It is produced in fread's C code where the very nice (but R level) txtProgressBar and tkProgressBar are not easily available.
data.table
TRUE returns a data.table
. FALSE returns a data.frame
. The default for this argument can be changed with options(datatable.fread.datatable=FALSE)
.
nThread
The number of threads to use. Experiment to see what works best for your data on your hardware.
logical01
If TRUE a column containing only 0s and 1s will be read as logical, otherwise as integer.
keepLeadingZeros
If TRUE a column containing numeric data with leading zeros will be read as character, otherwise leading zeros will be removed and converted to numeric.
yaml
If TRUE
, fread
will attempt to parse (using yaml.load
) the top of the input as YAML, and further to glean parameters relevant to improving the performance of fread
on the data itself. The entire YAML section is returned as parsed into a list
in the yaml_metadata
attribute. See Details
.
autostart
Deprecated and ignored with warning. Please use skip
instead.
tmpdir
Directory to use as the tmpdir
argument for any tempfile
calls, e.g. when the input is a URL or a shell command. The default is tempdir()
which can be controlled by setting TMPDIR
before starting the R session; see base::tempdir
.
tz
Relevant to datetime values which have no Z or UTC-offset at the end, i.e. unmarked datetime, as written by utils::write.csv
. The default tz="UTC"
reads unmarked datetime as UTC POSIXct efficiently. tz=""
reads unmarked datetime as type character (slowly) so that as.POSIXct
can interpret (slowly) the character datetimes in local timezone; e.g. by using "POSIXct"
in colClasses=
. Note that fwrite()
by default writes datetime in UTC including the final Z and therefore fwrite
's output will be read by fread
consistently and quickly without needing to use tz=
or colClasses=
. If the TZ
environment variable is set to "UTC"
(or ""
on non-Windows where unset vs ‘""' is significant) then the R session’s timezone is already UTC and tz=""
will result in unmarked datetimes being read as UTC POSIXct. For more information, please see the news items from v1.13.0 and v1.14.0.