emit csv when the first line lacks some of the fields

bin/csv.js

@@ -1,5 +1,7 @@
 #!/usr/bin/env node
 
+var fs = require('fs');
+
 // Render lines of JSON as CSV.
 
 var by = process.argv[2];
@@ -11,6 +13,21 @@ function csvRecord(record){
     return json.substr(1,json.length-2);
 }
 
+function getHeaders(stream){
+    return new Promise(function(yay, nay){
+        var headers = {};
+        parseStream(stream)
+        .on('jline', function(record){
+            Object.keys(record).forEach(function(key){
+                headers[key] = null;
+            })
+        })
+        .on('end', function(){
+            yay(Object.keys(headers))
+        })
+    });
+}
+
 function streamToCsv(stream){
     var headers;
     return parseStream(stream)
@@ -33,8 +50,20 @@ if(require.main === module) {
   }
   process.stdout.on('error',process.exit);
   console.log.apply(null,['#'].concat(process.argv));
-  streamToCsv(process.stdin)
-  .on('csvHeader', console.log)
-  .on('csv'      , console.log);
+  var infile = process.argv[2];
+  if (infile === undefined) {
+      streamToCsv(process.stdin)
+      .on('csvHeader', console.log)
+      .on('csv'      , console.log);
+  } else {
+      getHeaders(fs.createReadStream(infile))
+      .then(function(headers){
+          console.log(csvRecord(headers));
+          parseStream(fs.createReadStream(infile))
+          .on('jline', function(record){
+            console.log(csvRecord(headers.map(function(col){return (record[col] === undefined)?null:record[col];})));
+          });
+    });
+  }
 }
 

bin/csv.md

@@ -3,7 +3,9 @@ csv.md
 
 Convert JSON lines to CSV.
 
-This uses the keys of the first line as the column headings.
+When reading from stdin, this uses the keys of the first line as the column headings.
+
+When the input file is given as an argument it is scanned twice, once to collect all the keys and a second time to emit the data.
 
 ## Command line:
 

package.json

@@ -1,6 +1,6 @@
 {
   "name": "jline",
-  "version": "0.0.45",
+  "version": "0.0.46",
   "description": "Sort, grep and join files where every line is JSON.",
   "main": "index.js",
   "bin": {