read.table {base}R Documentation

Data Input

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 = ".",
           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 = "#")

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, ...)

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, 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 an EOF signal, Ctrl-D on Unix and Ctrl-Z on Windows.)
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 vector of strings which are to be interpreted as NA values. Blank fields are also considered to be missing values.
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.
... Further arguments to read.table.

Details

A field or line is ‘blank’ if it contains nothing (except whitespace is 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 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.

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.
This function is the principal means of reading tabular data into R.

Note

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).

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.


[Package base version 2.1.0 Index]