Initial data commit

Task/CSV-data-manipulation/JavaScript/csv-data-manipulation-2.js

@@ -0,0 +1,41 @@
+const fs = require('fs');
+
+// formats for the data parameter in the function below: {col1: array | function, col2: array | function}
+
+function addCols(path, data) {
+  let csv = fs.readFileSync(path, 'utf8');
+  csv = csv.split('\n').map(line => line.trim());
+  let colNames = Object.keys(data);
+  for (let i = 0; i < colNames.length; i++) {
+    let c = colNames[i];
+    if (typeof data[c] === 'function') {
+      csv = csv.map((line, idx) => idx === 0
+        ? line + ',' + c
+        : line + ',' + data[c](line, idx)
+      );
+    } else if (Array.isArray(data[c])) {
+      csv = csv.map((line, idx) => idx === 0
+        ? line + ',' + c
+        : line + ',' + data[c][idx - 1]
+      );
+    }
+  }
+  fs.createWriteStream(path, {
+    flag: 'w',
+    defaultEncoding: 'utf8'
+  }).end(csv.join('\n'));
+}
+
+addCols('test.csv', {
+    sum: function (line, idx) {
+      let s = 0;
+      line = line.split(',').map(d => +(d.trim()));
+      for (let i = 0; i < line.length; i++) {
+        s += line[i];
+      }
+      return s;
+    },
+    id: function(line, idx) {
+      return idx;
+    }
+  });