Description
Reads a file in table format and creates a data frame from it, with cases corresponding to lines and variables to fields in the file.
Usage
read.table(file, header = FALSE, sep = "", quote = "\"'", dec = ".", numerals = c("allow.loss", "warn.loss", "no.loss"), row.names, col.names, as.is = !stringsAsFactors, na.strings = "NA", colClasses = NA, nrows = -1, skip = 0, check.names = TRUE, fill = !blank.lines.skip, strip.white = FALSE, blank.lines.skip = TRUE, comment.char = "#", allowEscapes = FALSE, flush = FALSE, stringsAsFactors = default.stringsAsFactors(), fileEncoding = "", encoding = "unknown", text, skipNul = FALSE)read.csv(file, header = TRUE, sep = ",", quote = "\"", dec = ".", fill = TRUE, comment.char = "", …)
read.csv2(file, header = TRUE, sep = ";", quote = "\"", dec = ",", fill = TRUE, comment.char = "", …)
read.delim(file, header = TRUE, sep = "\t", quote = "\"", dec = ".", fill = TRUE, comment.char = "", …)
read.delim2(file, header = TRUE, sep = "\t", quote = "\"", dec = ",", fill = TRUE, comment.char = "", …)
Arguments
file
the name of the file which the data are to be read from. Each row of the table appears as one line of the file. If it does not contain an absolute path, the file name is relative to the current working directory, Alternatively, getwd()
. Tilde-expansion is performed where supported. This can be a compressed file (see file
).file
can be a readable text-mode connection (which will be opened for reading if necessary, and if so close
d (and hence destroyed) at the end of the function call). (If stdin()
is used, the prompts for lines may be somewhat confusing. Terminate input with a blank line or an EOF signal, Ctrl-D
on Unix and Ctrl-Z
on Windows. Any pushback on stdin()
will be cleared before return.)file
can also be a complete URL. (For the supported URL schemes, see the ‘URLs’ section of the help for url
.)
header
a logical value indicating whether the file contains the names of the variables as its first line. If missing, the value is determined from the file format: header
is set to TRUE
if and only if the first row contains one fewer field than the number of columns.
sep
the field separator character. Values on each line of the file are separated by this character. If sep = ""
(the default for read.table
) the separator is ‘white space’, that is one or more spaces, tabs, newlines or carriage returns.
quote
the set of quoting characters. To disable quoting altogether, use quote = ""
. See scan
for the behaviour on quotes embedded in quotes. Quoting is only considered for columns read as character, which is all of them unless colClasses
is specified.
dec
the character used in the file for decimal points.
numerals
string indicating how to convert numbers whose conversion to double precision would lose accuracy, see type.convert
. Can be abbreviated. (Applies also to complex-number inputs.)
row.names
a vector of row names. This can be a vector giving the actual row names, or a single number giving the column of the table which contains the row names, or character string giving the name of the table column containing the row names. If there is a header and the first row contains one fewer field than the number of columns, the first column in the input is used for the row names. Otherwise if row.names
is missing, the rows are numbered.
Using row.names = NULL
forces row numbering. Missing or NULL
row.names
generate row names that are considered to be ‘automatic’ (and not preserved by as.matrix
).
col.names
a vector of optional names for the variables. The default is to use "V"
followed by the column number.
as.is
the default behavior of Note: to suppress all conversions including those of numeric columns, set Note that read.table
is to convert character variables (which are not converted to logical, numeric or complex) to factors. The variable as.is
controls the conversion of columns not otherwise specified by colClasses
. Its value is either a vector of logicals (values are recycled if necessary), or a vector of numeric or character indices which specify which columns should not be converted to factors.colClasses = "character"
.as.is
is specified per column (not per variable) and so includes the column of row names (if any) and any columns to be skipped.
na.strings
a character vector of strings which are to be interpreted as NA
values. Blank fields are also considered to be missing values in logical, integer, numeric and complex fields. Note that the test happens after white space is stripped from the input, so na.strings
values may need their own white space stripped in advance.
colClasses
character. A vector of classes to be assumed for the columns. If unnamed, recycled as necessary. If named, names are matched with unspecified values being taken to be Possible values are Note that NA
.NA
(the default, when type.convert
is used), "NULL"
(when the column is skipped), one of the atomic vector classes (logical, integer, numeric, complex, character, raw), or "factor"
, "Date"
or "POSIXct"
. Otherwise there needs to be an as
method (from package methods) for conversion from "character"
to the specified formal class.colClasses
is specified per column (not per variable) and so includes the column of row names (if any).
nrows
integer: the maximum number of rows to read in. Negative and other invalid values are ignored.
skip
integer: the number of lines of the data file to skip before beginning to read data.
check.names
logical. If TRUE
then the names of the variables in the data frame 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.
fill
logical. If TRUE
then in case the rows have unequal length, blank fields are implicitly added. See ‘Details’.
strip.white
logical. Used only when sep
has been specified, and allows the stripping of leading and trailing white space from unquoted character
fields (numeric
fields are always stripped). See scan
for further details (including the exact meaning of ‘white space’), remembering that the columns may include the row names.
blank.lines.skip
logical: if TRUE
blank lines in the input are ignored.
comment.char
character: a character vector of length one containing a single character or an empty string. Use ""
to turn off the interpretation of comments altogether.
allowEscapes
logical. Should C-style escapes such as \n be processed or read verbatim (the default)? Note that if not within quotes these could be interpreted as a delimiter (but not as a comment character). For more details see scan
.
flush
logical: if TRUE
, scan
will flush to the end of the line after reading the last of the fields requested. This allows putting comments after the last field.
stringsAsFactors
logical: should character vectors be converted to factors? Note that this is overridden by as.is
and colClasses
, both of which allow finer control.
fileEncoding
character string: if non-empty declares the encoding used on a file (not a connection) so the character data can be re-encoded. See the ‘Encoding’ section of the help for file
, the ‘R Data Import/Export Manual’ and ‘Note’.
encoding
encoding to be assumed for input strings. It is used to mark character strings as known to be in Latin-1 or UTF-8 (see Encoding
): it is not used to re-encode the input, but allows R to handle encoded strings in their native encoding (if one of those two). See ‘Value’ and ‘Note’.
text
character string: if file
is not supplied and this is, then data are read from the value of text
via a text connection. Notice that a literal string can be used to include (small) data sets within R code.
skipNul
logical: should nuls be skipped?
…
Further arguments to be passed to read.table
.
Value
A data frame (data.frame
) containing a representation of the data in the file.
Empty input is an error unless col.names
is specified, when a 0-row data frame is returned: similarly giving just a header line if header = TRUE
results in a 0-row data frame. Note that in either case the columns will be logical unless colClasses
was supplied.
Character strings in the result (including factor levels) will have a declared encoding if encoding
is "latin1"
or "UTF-8"
.
Memory usage
These functions can use a surprising amount of memory when reading large files. There is extensive discussion in the ‘R Data Import/Export’ manual, supplementing the notes here. Less memory will be used if Using Using colClasses
is specified as one of the six atomic vector classes. This can be particularly so when reading a column that takes many distinct numeric values, as storing each distinct value as a character string can take up to 14 times as much memory as storing it as an integer.nrows
, even as a mild over-estimate, will help memory usage.comment.char = ""
will be appreciably faster than the read.table
default.read.table
is not the right tool for reading large matrices, especially those with many columns: it is designed to read data frames which may have columns of very different classes. Use scan
instead for matrices.
Details
This function is the principal means of reading tabular data into R.
Unless colClasses
is specified, all columns are read as character columns and then converted using type.convert
to logical, integer, numeric, complex or (depending on as.is
) factor as appropriate. Quotes are (by default) interpreted in all fields, so a column of values like "42"
will result in an integer column.
A field or line is ‘blank’ if it contains nothing (except whitespace if no separator is specified) before a comment character or the end of the field or line.
If row.names
is not specified and the header line has one less entry than the number of columns, the first column is taken to be the row names. This allows data frames to be read in from the format in which they are printed. If row.names
is specified and does not refer to the first column, that column is discarded from such files.
The number of data columns is determined by looking at the first five lines of input (or the whole input if it has less than five lines), or from the length of col.names
if it is specified and is longer. This could conceivably be wrong if fill
or blank.lines.skip
are true, so specify col.names
if necessary (as in the ‘Examples’).
read.csv
and read.csv2
are identical to read.table
except for the defaults. They are intended for reading ‘comma separated value’ files (.csv
) or (read.csv2
) the variant used in countries that use a comma as decimal point and a semicolon as field separator. Similarly, read.delim
and read.delim2
are for reading delimited files, defaulting to the TAB character for the delimiter. Notice that header = TRUE
and fill = TRUE
in these variants, and that the comment character is disabled.
The rest of the line after a comment character is skipped; quotes are not processed in comments. Complete comment lines are allowed provided blank.lines.skip = TRUE
; however, comment lines prior to the header must have the comment character in the first non-blank column.
Quoted fields with embedded newlines are supported except after a comment character. Embedded nuls are unsupported: skipping them (with skipNul = TRUE
) may work.
References
Chambers, J. M. (1992) Data for models. Chapter 3 of Statistical Models in S eds J. M. Chambers and T. J. Hastie, Wadsworth & Brooks/Cole.
See Also
The ‘R Data Import/Export’ manual.
scan
, type.convert
, read.fwf
for reading fixed width formatted input; write.table
; data.frame
.
count.fields
can be useful to determine problems with reading files which result in reports of incorrect record lengths (see the ‘Examples’ below).
https://tools.ietf.org/html/rfc4180 for the IANA definition of CSV files (which requires comma as separator and CRLF line endings).
Examples
# NOT RUN {## using count.fields to handle unknown maximum number of fields## when fill = TRUEtest1 <- c(1:5, "6,7", "8,9,10")tf <- tempfile()writeLines(test1, tf)read.csv(tf, fill = TRUE) # 1 columnncol <- max(count.fields(tf, sep = ","))read.csv(tf, fill = TRUE, header = FALSE, col.names = paste0("V", seq_len(ncol)))unlink(tf)## "Inline" data set, using text=## Notice that leading and trailing empty lines are auto-trimmedread.table(header = TRUE, text = "a b1 23 4")# }
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