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node_modules/vega-transforms/src/Flatten.js

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+import {fieldNames} from './util/util';
+import {Transform, derive} from 'vega-dataflow';
+import {inherits} from 'vega-util';
+
+/**
+ * Flattens array-typed field values into new data objects.
+ * If multiple fields are specified, they are treated as parallel arrays,
+ * with output values included for each matching index (or null if missing).
+ * @constructor
+ * @param {object} params - The parameters for this operator.
+ * @param {Array<function(object): *>} params.fields - An array of field
+ *   accessors for the tuple fields that should be flattened.
+ * @param {string} [params.index] - Optional output field name for index
+ *   value. If unspecified, no index field is included in the output.
+ * @param {Array<string>} [params.as] - Output field names for flattened
+ *   array fields. Any unspecified fields will use the field name provided
+ *   by the fields accessors.
+ */
+export default function Flatten(params) {
+  Transform.call(this, [], params);
+}
+
+Flatten.Definition = {
+  'type': 'Flatten',
+  'metadata': {'generates': true},
+  'params': [
+    { 'name': 'fields', 'type': 'field', 'array': true, 'required': true },
+    { 'name': 'index', 'type': 'string' },
+    { 'name': 'as', 'type': 'string', 'array': true }
+  ]
+};
+
+var prototype = inherits(Flatten, Transform);
+
+prototype.transform = function(_, pulse) {
+  var out = pulse.fork(pulse.NO_SOURCE),
+      fields = _.fields,
+      as = fieldNames(fields, _.as || []),
+      index = _.index || null,
+      m = as.length;
+
+  // remove any previous results
+  out.rem = this.value;
+
+  // generate flattened tuples
+  pulse.visit(pulse.SOURCE, function(t) {
+    var arrays = fields.map(f => f(t)),
+        maxlen = arrays.reduce((l, a) => Math.max(l, a.length), 0),
+        i = 0, j, d, v;
+
+    for (; i<maxlen; ++i) {
+      d = derive(t);
+      for (j=0; j<m; ++j) {
+        d[as[j]] = (v = arrays[j][i]) == null ? null : v;
+      }
+      if (index) {
+        d[index] = i;
+      }
+      out.add.push(d);
+    }
+  });
+
+  this.value = out.source = out.add;
+  if (index) out.modifies(index);
+  return out.modifies(as);
+};