R: Return melted data for each token in a fixed width file

melt_fwf {readr} | R Documentation

## Return melted data for each token in a fixed width file

### Description

For certain non-rectangular data formats, it can be useful to parse the data into a melted format where each row represents a single token.

### Usage

    melt_fwf(
      file,
      col_positions,
      locale = default_locale(),
      na = c("", "NA"),
      comment = "",
      trim_ws = TRUE,
      skip = 0,
      n_max = Inf,
      progress = show_progress(),
      skip_empty_rows = FALSE
    )

### Arguments

`file` | Either a path to a file, a connection, or literal data (either a single string or a raw vector). Files ending in `.gz`, `.bz2`, `.xz`, or `.zip` will be automatically uncompressed. Files starting with `http://`, `https://`, `ftp://`, or `ftps://` will be automatically downloaded. Remote gz files can also be automatically downloaded and decompressed. Literal data is most useful for examples and tests. It must contain at least one new line to be recognised as data (instead of a path) or be a vector of greater than length 1. Using a value of `clipboard()` will read from the system clipboard.
`col_positions` | Column positions, as created by `fwf_empty()`, `fwf_widths()` or `fwf_positions()`. To read in only selected fields, use `fwf_positions()`. If the width of the last column is variable (a ragged fwf file), supply the last end position as NA.
`locale` | The locale controls defaults that vary from place to place. The default locale is US-centric (like R), but you can use `locale()` to create your own locale that controls things like the default time zone, encoding, decimal mark, big mark, and day/month names.
`na` | Character vector of strings to interpret as missing values. Set this option to `character()` to indicate no missing values.
`comment` | A string used to identify comments. Any text after the comment characters will be silently ignored.
`trim_ws` | Should leading and trailing whitespace be trimmed from each field before parsing it?
`skip` | Number of lines to skip before reading data.
`n_max` | Maximum number of records to read.
`progress` | Display a progress bar? By default it will only display in an interactive session and not while knitting a document. The display is updated every 50,000 values and will only display if estimated reading time is 5 seconds or more. The automatic progress bar can be disabled by setting option `readr.show_progress` to `FALSE`.
`skip_empty_rows` | Should blank rows be ignored altogether? i.e. If this option is `TRUE` then blank rows will not be represented at all. If it is `FALSE` then they will be represented by `NA` values in all the columns.

### Details

`melt_fwf()` parses each token of a fixed width file into a single row, but it still requires that each field is in the same in every row of the source file.

### See Also

`melt_table()` to melt fixed width files where each column is separated by whitespace, and `read_fwf()` for the conventional way to read rectangular data from fixed width files.

### Examples

    fwf_sample <- readr_example("fwf-sample.txt")
    cat(read_lines(fwf_sample))

    # You can specify column positions in several ways:
    # 1. Guess based on position of empty columns
    melt_fwf(fwf_sample, fwf_empty(fwf_sample, col_names = c("first", "last", "state", "ssn")))
    # 2. A vector of field widths
    melt_fwf(fwf_sample, fwf_widths(c(20, 10, 12), c("name", "state", "ssn")))
    # 3. Paired vectors of start and end positions
    melt_fwf(fwf_sample, fwf_positions(c(1, 30), c(10, 42), c("name", "ssn")))
    # 4. Named arguments with start and end positions
    melt_fwf(fwf_sample, fwf_cols(name = c(1, 10), ssn = c(30, 42)))
    # 5. Named arguments with column widths
    melt_fwf(fwf_sample, fwf_cols(name = 20, state = 10, ssn = 12))

[Package readr version 1.4.0 Index]