/usr/lib/swi-prolog/doc/Manual/csv.html

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<h2 id="sec:csv"><a id="sec:A.9"><span class="sec-nr">A.9</span> <span class="sec-title">library(csv): 
Process CSV (Comma-Separated Values) data</span></a></h2>

<p><a id="sec:csv"></a>

<dl class="tags">
<dt class="tag">See also</dt>
<dd>
RFC 4180</dd>
<dt class="mtag">To be done</dt>
<dd>
- Implement immediate assert of the data to avoid possible stack 
overflows. <br>
- Writing creates an intermediate code-list, possibly overflowing 
resources. This waits for pure output!
</dd>
</dl>

<p>This library parses and generates CSV data. CSV data is represented 
in Prolog as a list of rows. Each row is a compound term, where all rows 
have the same name and arity.

<dl class="latex">
<dt class="pubdef"><span class="pred-tag">[det]</span><a id="csv_read_file/2"><strong>csv_read_file</strong>(<var>+File, 
-Rows</var>)</a></dt>
<dt class="pubdef"><span class="pred-tag">[det]</span><a id="csv_read_file/3"><strong>csv_read_file</strong>(<var>+File, 
-Rows, +Options</var>)</a></dt>
<dd class="defbody">
Read a CSV file into a list of rows. Each row is a Prolog term with the 
same arity. <var>Options</var> is handed to <a class="pred" href="csv.html#csv/4">csv/4</a>. 
Remaining options are processed by <a class="pred" href="pio.html#phrase_from_file/3">phrase_from_file/3</a>. 
The default separator depends on the file name extension and is <code>\t</code> 
for
<code>.tsv</code> files and <code>,</code> otherwise.

<p>Suppose we want to create a predicate <span class="pred-ext">table/6</span> 
from a CSV file that we know contains 6 fields per record. This can be 
done using the code below. Without the option <code>arity(6)</code>, 
this would generate a predicate table/N, where N is the number of fields 
per record in the data.

<pre class="code">
?- csv_read_file(File, Rows, [functor(table), arity(6)]),
   maplist(assert, Rows).
</pre>

</dd>
<dt class="pubdef"><span class="pred-tag">[det]</span><a id="csv/3"><strong>csv</strong>(<var>?Rows</var>)</a><code>//</code></dt>
<dt class="pubdef"><span class="pred-tag">[det]</span><a id="csv/4"><strong>csv</strong>(<var>?Rows, 
+Options</var>)</a><code>//</code></dt>
<dd class="defbody">
Prolog DCG to `read/write' CSV data. <var>Options</var>:

<dl class="latex">
<dt><strong>separator</strong>(<var>+Code</var>)</dt>
<dd class="defbody">
The comma-separator. Must be a character code. Default is (of course) 
the comma. Character codes can be specified using the 0' notion. E.g., 
using <code>separator(0';)</code> parses a semicolon separated file.
</dd>
<dt><strong>ignore_quotes</strong>(<var>+Boolean</var>)</dt>
<dd class="defbody">
If <code>true</code> (default false), threat double quotes as a normal 
character.
</dd>
<dt><strong>strip</strong>(<var>+Boolean</var>)</dt>
<dd class="defbody">
If <code>true</code> (default <code>false</code>), strip leading and 
trailing blank space. RFC4180 says that blank space is part of the data.
</dd>
<dt><strong>convert</strong>(<var>+Boolean</var>)</dt>
<dd class="defbody">
If <code>true</code> (default), use <a class="pred" href="manipatom.html#name/2">name/2</a> 
on the field data. This translates the field into a number if possible.
</dd>
<dt><strong>functor</strong>(<var>+Atom</var>)</dt>
<dd class="defbody">
Functor to use for creating row terms. Default is <code>row</code>.
</dd>
<dt><strong>arity</strong>(<var>?Arity</var>)</dt>
<dd class="defbody">
Number of fields in each row. This predicate raises a <code>domain_error(row_arity(Expected), Found)</code> 
if a row is found with different arity.
</dd>
<dt><strong>match_arity</strong>(<var>+Boolean</var>)</dt>
<dd class="defbody">
If <code>false</code> (default <code>true</code>), do not reject CSV 
files where lines provide a varying number of fields (columns). This can 
be a work-around to use some incorrect CSV files.
</dd>
</dl>

</dd>
<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="csv_read_file_row/3"><strong>csv_read_file_row</strong>(<var>+File, 
-Row, +Options</var>)</a></dt>
<dd class="defbody">
True when <var>Row</var> is a row in <var>File</var>. First unifies <var>Row</var> 
with the first row in <var>File</var>. Backtracking yields the second, 
... row. This interface is an alternative to <a class="pred" href="csv.html#csv_read_file/3">csv_read_file/3</a> 
that avoids loading all rows in memory. Note that this interface does 
not guarantee that all rows in <var>File</var> have the same arity.

<p>In addition to the options of <a class="pred" href="csv.html#csv_read_file/3">csv_read_file/3</a>, 
this predicate processes the option:

<dl class="latex">
<dt><strong>line</strong>(<var>-Line</var>)</dt>
<dd class="defbody">
<var>Line</var> is unified with the 1-based line-number from which <var>Row</var> 
is read. Note that <var>Line</var> is not the physical line, but rather 
the
<i>logical</i> record number.
</dd>
</dl>

<dl class="tags">
<dt class="tag">To be done</dt>
<dd>
Input is read line by line. If a record separator is embedded in a 
quoted field, parsing the record fails and another line is added to the 
input. This does not nicely deal with other reasons why parsing the row 
may fail.
</dd>
</dl>

</dd>
<dt class="pubdef"><span class="pred-tag">[det]</span><a id="csv_write_file/2"><strong>csv_write_file</strong>(<var>+File, 
+Data</var>)</a></dt>
<dt class="pubdef"><span class="pred-tag">[det]</span><a id="csv_write_file/3"><strong>csv_write_file</strong>(<var>+File, 
+Data, +Options</var>)</a></dt>
<dd class="defbody">
Write a list of Prolog terms to a CSV file. <var>Options</var> are given 
to <a class="pred" href="csv.html#csv/4">csv/4</a>. Remaining options 
are given to <a class="pred" href="IO.html#open/4">open/4</a>. The 
default separator depends on the file name extension and is <code>\t</code> 
for
<code>.tsv</code> files and <code>,</code> otherwise.</dd>
<dt class="pubdef"><span class="pred-tag">[det]</span><a id="csv_write_stream/3"><strong>csv_write_stream</strong>(<var>+Stream, 
+Data, +Options</var>)</a></dt>
<dd class="defbody">
Write the rows in <var>Data</var> to <var>Stream</var>. This is similar 
to
<a class="pred" href="csv.html#csv_write_file/3">csv_write_file/3</a>, 
but can deal with data that is produced incrementally. The example below 
saves all answers from the predicate <span class="pred-ext">data/3</span> 
to File.

<pre class="code">
save_data(File) :-
   setup_call_cleanup(
       open(File, write, Out),
       forall(data(C1,C2,C3),
              csv_write_stream(Out, [row(C1,C2,C3)], [])),
       close(Out)),
</pre>

<p></dd>
</dl>

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swi-prolog-nox 6.6.4-2ubuntu1 / usr / lib / swi-prolog / doc / Manual / csv.html
