| read.table {base} | R Documentation |
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.
read.table(file, header = FALSE, sep = "", quote = "\"'", dec = ".",
row.names, col.names, as.is = FALSE, 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)
read.csv(file, header = TRUE, sep = ",", quote="\"", dec=".",
fill = TRUE, ...)
read.csv2(file, header = TRUE, sep = ";", quote="\"", dec=",",
fill = TRUE, ...)
read.delim(file, header = TRUE, sep = "\t", quote="\"", dec=".",
fill = TRUE, ...)
read.delim2(file, header = TRUE, sep = "\t", quote="\"", dec=",",
fill = TRUE, ...)
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,
getwd(). Tilde-expansion is performed where supported.
Alternatively, file can be a connection, which
will be opened if necessary, and if so closed 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.
To read a data file not in the current encoding (for example a Latin-1 file in a UTF-8 locale or conversely) use a file connection setting the encoding argument.
|
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. |
dec |
the character used in the file for decimal points. |
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.
|
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 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.
Note: to suppress all conversions including those of numeric columns, set colClasses = "character".
Note that 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. |
colClasses |
character. A vector of classes to be assumed for
the columns. Recycled as necessary, or if the character vector is
named, unspecified values are taken to be NA.
Possible values are NA (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.
Note that colClasses is specified per column (not per
variable) and so includes the column of row names (if any).
|
nrows |
the maximum number of rows to read in. Negative values are ignored. |
skip |
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 character fields (numeric fields
are always stripped). See scan for further details,
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. |
... |
Further arguments to read.table. |
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 file 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.
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.
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.
As from R 1.9.0 quoted fields with embedded newlines are supported except after a comment character.
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.
This function is the principal means of reading tabular data into R.
The columns referred to in as.is and colClasses include
the column of row names (if any).
Less memory will be used if colClasses is specified as one of
the six atomic vector classes.
Using nrows, even as a mild over-estimate, will help memory
usage.
Using comment.char = "" will be appreciably faster.
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.
Prior to version 1.9.0, underscores were not valid in variable names,
and code that relies on them being converted to dots will no longer
work. The simplest workaround is to use
names(d) <- gsub("_", ".", names(d)),
or, avoiding the (small) risk of creating duplicate names,
names(d) <- make.names(gsub("_", ".", names(d)), unique=TRUE).
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.
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.