fix: Fix spread column generation. (#209)

src/engine/spread.js

@@ -43,12 +43,11 @@ export default function(table, { names, exprs, ops = [] }, options = {}) {
 function spread(table, get, limit) {
   const nrows = table.totalRows();
   const columns = [];
-  let j = -1;
 
   table.scan((row, data) => {
     const values = toArray(get(row, data));
     const n = Math.min(values.length, limit);
-    while (++j < n) {
+    while (columns.length < n) {
       columns.push(Array(nrows).fill(NULL));
     }
     for (let i = 0; i < n; ++i) {

test/verbs/spread-test.js

@@ -97,4 +97,34 @@ tape('spread ignores as option with multi column input', t => {
     b_2: [ 'bop', 'baz', undefined, 'bar' ]
   }, 'spread data with as');
   t.end();
-});
+});
+
+tape('spread handles arrays of varying length', t => {
+  const data1 = {
+    u: [
+      ['A', 'B', 'C'],
+      ['D', 'E']
+    ]
+  };
+  const data2 = {
+    u: data1.u.slice().reverse()
+  };
+  const obj = [
+    { u_1: 'A', u_2: 'B', u_3: 'C' },
+    { u_1: 'D', u_2: 'E', u_3: undefined }
+  ];
+
+  t.deepEqual(
+    table(data1).spread('u').objects(),
+    obj,
+    'spread data, larger first'
+  );
+
+  t.deepEqual(
+    table(data2).spread('u').objects(),
+    obj.slice().reverse(),
+    'spread data, smaller first'
+  );
+
+  t.end();
+});