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Edit File: melt_delim_chunked.html
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><title>R: Melt a delimited file by chunks</title> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <link rel="stylesheet" type="text/css" href="R.css" /> </head><body> <table width="100%" summary="page for melt_delim_chunked {readr}"><tr><td>melt_delim_chunked {readr}</td><td style="text-align: right;">R Documentation</td></tr></table> <h2>Melt a delimited file by chunks</h2> <h3>Description</h3> <p>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. </p> <h3>Usage</h3> <pre> melt_delim_chunked(file, callback, chunk_size = 10000, delim, quote = "\"", escape_backslash = FALSE, escape_double = TRUE, locale = default_locale(), na = c("", "NA"), quoted_na = TRUE, comment = "", trim_ws = FALSE, skip = 0, progress = show_progress(), skip_empty_rows = FALSE) melt_csv_chunked(file, callback, chunk_size = 10000, locale = default_locale(), na = c("", "NA"), quoted_na = TRUE, quote = "\"", comment = "", trim_ws = TRUE, skip = 0, progress = show_progress(), skip_empty_rows = FALSE) melt_csv2_chunked(file, callback, chunk_size = 10000, locale = default_locale(), na = c("", "NA"), quoted_na = TRUE, quote = "\"", comment = "", trim_ws = TRUE, skip = 0, progress = show_progress(), skip_empty_rows = FALSE) melt_tsv_chunked(file, callback, chunk_size = 10000, locale = default_locale(), na = c("", "NA"), quoted_na = TRUE, quote = "\"", comment = "", trim_ws = TRUE, skip = 0, progress = show_progress(), skip_empty_rows = FALSE) </pre> <h3>Arguments</h3> <table summary="R argblock"> <tr valign="top"><td><code>file</code></td> <td> <p>Either a path to a file, a connection, or literal data (either a single string or a raw vector). </p> <p>Files ending in <code>.gz</code>, <code>.bz2</code>, <code>.xz</code>, or <code>.zip</code> will be automatically uncompressed. Files starting with <code>http://</code>, <code>https://</code>, <code>ftp://</code>, or <code>ftps://</code> will be automatically downloaded. Remote gz files can also be automatically downloaded and decompressed. </p> <p>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. </p> <p>Using a value of <code><a href="clipboard.html">clipboard()</a></code> will read from the system clipboard.</p> </td></tr> <tr valign="top"><td><code>callback</code></td> <td> <p>A callback function to call on each chunk</p> </td></tr> <tr valign="top"><td><code>chunk_size</code></td> <td> <p>The number of rows to include in each chunk</p> </td></tr> <tr valign="top"><td><code>delim</code></td> <td> <p>Single character used to separate fields within a record.</p> </td></tr> <tr valign="top"><td><code>quote</code></td> <td> <p>Single character used to quote strings.</p> </td></tr> <tr valign="top"><td><code>escape_backslash</code></td> <td> <p>Does the file use backslashes to escape special characters? This is more general than <code>escape_double</code> as backslashes can be used to escape the delimiter character, the quote character, or to add special characters like <code>\n</code>.</p> </td></tr> <tr valign="top"><td><code>escape_double</code></td> <td> <p>Does the file escape quotes by doubling them? i.e. If this option is <code>TRUE</code>, the value <code>""""</code> represents a single quote, <code>\"</code>.</p> </td></tr> <tr valign="top"><td><code>locale</code></td> <td> <p>The locale controls defaults that vary from place to place. The default locale is US-centric (like R), but you can use <code><a href="locale.html">locale()</a></code> to create your own locale that controls things like the default time zone, encoding, decimal mark, big mark, and day/month names.</p> </td></tr> <tr valign="top"><td><code>na</code></td> <td> <p>Character vector of strings to interpret as missing values. Set this option to <code>character()</code> to indicate no missing values.</p> </td></tr> <tr valign="top"><td><code>quoted_na</code></td> <td> <p>Should missing values inside quotes be treated as missing values (the default) or strings.</p> </td></tr> <tr valign="top"><td><code>comment</code></td> <td> <p>A string used to identify comments. Any text after the comment characters will be silently ignored.</p> </td></tr> <tr valign="top"><td><code>trim_ws</code></td> <td> <p>Should leading and trailing whitespace be trimmed from each field before parsing it?</p> </td></tr> <tr valign="top"><td><code>skip</code></td> <td> <p>Number of lines to skip before reading data.</p> </td></tr> <tr valign="top"><td><code>progress</code></td> <td> <p>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 <code>readr.show_progress</code> to <code>FALSE</code>.</p> </td></tr> <tr valign="top"><td><code>skip_empty_rows</code></td> <td> <p>Should blank rows be ignored altogether? i.e. If this option is <code>TRUE</code> then blank rows will not be represented at all. If it is <code>FALSE</code> then they will be represented by <code>NA</code> values in all the columns.</p> </td></tr> </table> <h3>Details</h3> <p><code>melt_delim_chunked()</code> and the specialisations <code>melt_csv_chunked()</code>, <code>melt_csv2_chunked()</code> and <code>melt_tsv_chunked()</code> read files by a chunk of rows at a time, executing a given function on one chunk before reading the next. </p> <h3>See Also</h3> <p>Other chunked: <code><a href="callback.html">callback</a></code>, <code><a href="read_delim_chunked.html">read_delim_chunked</a></code>, <code><a href="read_lines_chunked.html">read_lines_chunked</a></code> </p> <h3>Examples</h3> <pre> # Cars with 3 gears f <- function(x, pos) subset(x, data_type == "integer") melt_csv_chunked(readr_example("mtcars.csv"), DataFrameCallback$new(f), chunk_size = 5) </pre> <hr /><div style="text-align: center;">[Package <em>readr</em> version 1.3.1 <a href="00Index.html">Index</a>]</div> </body></html>