Add an example which shows how the write function can be used to dupl…

…icate headers.

samples/duplicate-headers.in

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+ts,year,ms,chars,age,date
+20322051544,1979.0,8.8017226E7,ABC,45,2000-01-01
+28392898392,1974.0,8.8392926E7,DEF,23,2050-11-27

samples/duplicate-headers.js

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+// CSV sample - Copyright jon seymour jon.seymour@gmail.com
+// node samples/duplicate-headers.js < samples/duplicate-headers.in
+
+//
+// This sample shows how the write function can be used
+// to write a new record into the output stream.
+//
+// In this rather contrived example, the first line read
+// is interpreted as a header and is inserted before
+// every other data line in the file.
+//
+
+  var
+    csv = require('csv'),
+    header;
+
+    process.stdin.resume();
+      csv()
+	.fromStream(process.stdin)
+	.toStream(process.stdout)
+	.transform(function(data){
+	  if (header) {
+	    this.write(header);
+	  } else {
+	    header=data;
+	    return null;
+	  }
+	  return data;
+	})
+	.on('error',function(error){
+	  console.log(error.message);
+	});
+
+//
+// expected output
+// 
+//ts,year,ms,chars,age,date
+//20322051544,1979.0,8.8017226E7,ABC,45,2000-01-01
+//ts,year,ms,chars,age,date
+//28392898392,1974.0,8.8392926E7,DEF,23,2050-11-27