# HG changeset patch
# User František Kučera <franta-hg@frantovo.cz>
# Date 1591612456 -7200
# Node ID 7029e6c477003de56356bf8e585ddbcdb8e59c8a
# Parent  b9bd0f06b4a130c3b94b99d119abd1dbc3126213
examples: improved Doing projection and restriction using cut and grep – add a chapter about CSV

diff -r b9bd0f06b4a1 -r 7029e6c47700 relpipe-data/examples-grep-cut-fstab.xml
--- a/relpipe-data/examples-grep-cut-fstab.xml	Sat Jun 06 13:22:57 2020 +0200
+++ b/relpipe-data/examples-grep-cut-fstab.xml	Mon Jun 08 12:34:16 2020 +0200
@@ -165,6 +165,59 @@
 			The <code>letters</code> relation stays rock steady and <code>relpipe-tr-cut 'numbers'</code> does not affect it in any way.
 		</p>
 		
+		<h2>Process CSV files</h2>
+		
+		<p>
+			There are various input filters (<code>relpipe-in-*</code>), one of them is <code>relpipe-in-csv</code>
+			which converts CSV files to relational format.
+			Thus we can process standard CSV files in our relational pipelines
+			and e.g. filter records that have certain value in certain column (<code>relpipe-tr-grep</code>)
+			or keep only certain columns (<code>relpipe-tr-cut</code>).
+		</p>
+		
+		<p>
+			We may have a <code>tasks.csv</code> file containing TODOs and FIXMEs:
+		</p>
+		
+		<pre><![CDATA["file","line","type","description"
+".hg/shelve-backup/posix_mq.patch","97","TODO","support also other encodings."
+".hg/shelve-backup/posix_mq.patch","163","TODO","support also other encodings."
+"src/FileAttributeFinder.h","79","TODO","optional whitespace trimming or substring"
+"src/FileAttributeFinder.h","80","TODO","custom encoding + read encoding from xattr"
+"src/FileAttributeFinder.h","83","TODO","allow custom error value or fallback to HEX/Base64"
+"streamlet-examples/streamlet-common.h","286","FIXME","correct error codes"
+…]]></pre>
+
+		<p>
+			And we can process it using this pipeline:
+		</p>
+		
+		<m:pre jazyk="bash"><![CDATA[cat tasks.csv \
+	| relpipe-in-csv \
+	| relpipe-tr-grep 'csv' 'type' 'FIXME' \
+	| relpipe-tr-cut 'csv' 'file|description' \
+	| relpipe-out-tabular]]></m:pre>
+	
+		<p>and get result like this:</p>
+	
+		<pre><![CDATA[csv:
+ ╭───────────────────────────────────────┬──────────────────────╮
+ │ file                         (string) │ description (string) │
+ ├───────────────────────────────────────┼──────────────────────┤
+ │ streamlet-examples/streamlet-common.h │ correct error codes  │
+ │ streamlet-examples/streamlet-common.h │ correct error codes  │
+ │ streamlet-examples/Streamlet.java     │ correct error codes  │
+ ╰───────────────────────────────────────┴──────────────────────╯
+Record count: 3]]></pre>
+
+	
+		<p>
+			We work with attribute (column) names, so there is no need to remember column numbers.
+			And thanks to regular expressions we can write elegant and powerful filters.
+		</p>
+
+
+		
 	</text>
 
 </stránka>