R: Data Input

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 = !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())

    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, `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`.
`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?
`...` | Further arguments to `read.table`.

### Details

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, 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.

### 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 2.4.1 Index]