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JavaScript's functional programming helper library.

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var _group = require('./_group.js');
var _has = require('./_has.js');

// Counts instances of an object that group by a certain criterion. Pass
// either a string attribute to count by, or a function that returns the
// criterion.
var countBy = _group(function(result, value, key) {
  if (_has(result, key)) result[key]++; else result[key] = 1;
});

module.exports = countBy;