// Invoke a method (with arguments) on every item in a collection._.invoke = function(obj, method) {var args = slice.call(arguments, 2);return _.map(obj, function(value) {return (method.call ? method || value : value[method]).apply(value, args);});};// Convenience version of a common use case of `map`: fetching a property._.pluck = function(obj, key) {return _.map(obj, function(value){ return value[key]; });};// Return the maximum element or (element-based computation)._.max = function(obj, iterator, context) {if (!iterator && _.isArray(obj)) return Math.max.apply(Math, obj);if (!iterator && _.isEmpty(obj)) return -Infinity;var result = {computed : -Infinity};each(obj, function(value, index, list) {var computed = iterator ? iterator.call(context, value, index, list) : value;computed >= result.computed && (result = {value : value, computed : computed});});return result.value;};// Return the minimum element (or element-based computation)._.min = function(obj, iterator, context) {if (!iterator && _.isArray(obj)) return Math.min.apply(Math, obj);if (!iterator && _.isEmpty(obj)) return Infinity;var result = {computed : Infinity};each(obj, function(value, index, list) {var computed = iterator ? iterator.call(context, value, index, list) : value;computed < result.computed && (result = {value : value, computed : computed});});return result.value;};// Shuffle an array._.shuffle = function(obj) {var shuffled = [], rand;each(obj, function(value, index, list) {if (index == 0) {shuffled[0] = value;} else {rand = Math.floor(Math.random() * (index + 1));shuffled[index] = shuffled[rand];shuffled[rand] = value;}});return shuffled;};// Sort the object's values by a criterion produced by an iterator._.sortBy = function(obj, iterator, context) {return _.pluck(_.map(obj, function(value, index, list) {return {value : value,criteria : iterator.call(context, value, index, list)};}).sort(function(left, right) {var a = left.criteria, b = right.criteria;return a < b ? -1 : a > b ? 1 : 0;}), 'value');};// Groups the object's values by a criterion produced by an iterator_.groupBy = function(obj, iterator) {var result = {};each(obj, function(value, index) {var key = iterator(value, index);(result[key] || (result[key] = [])).push(value);});return result;};// Use a comparator function to figure out at what index an object should// be inserted so as to maintain order. Uses binary search._.sortedIndex = function(array, obj, iterator) {iterator || (iterator = _.identity);var low = 0, high = array.length;while (low < high) {var mid = (low + high) >> 1;iterator(array[mid]) < iterator(obj) ? low = mid + 1 : high = mid;}return low;};// Safely convert anything iterable into a real, live array._.toArray = function(iterable) {if (!iterable) return [];if (iterable.toArray) return iterable.toArray();if (_.isArray(iterable)) return slice.call(iterable);if (_.isArguments(iterable)) return slice.call(iterable);return _.values(iterable);};// Return the number of elements in an object._.size = function(obj) {return _.toArray(obj).length;};

1 _.invoke([[5, 1, 7], [3, 2, 1]], 'sort');2 => [[1, 5, 7], [1, 2, 3]]

　// Array Functions// ---------------// Get the first element of an array. Passing **n** will return the first N// values in the array. Aliased as `head`. The **guard** check allows it to work// with `_.map`._.first = _.head = function(array, n, guard) {return (n != null) && !guard ? slice.call(array, 0, n) : array[0];};// Returns everything but the last entry of the array. Especcialy useful on// the arguments object. Passing **n** will return all the values in// the array, excluding the last N. The **guard** check allows it to work with// `_.map`._.initial = function(array, n, guard) {return slice.call(array, 0, array.length - ((n == null) || guard ? 1 : n));};// Get the last element of an array. Passing **n** will return the last N// values in the array. The **guard** check allows it to work with `_.map`._.last = function(array, n, guard) {return (n != null) && !guard ? slice.call(array, array.length - n) : array[array.length - 1];};// Returns everything but the first entry of the array. Aliased as `tail`.// Especially useful on the arguments object. Passing an **index** will return// the rest of the values in the array from that index onward. The **guard**// check allows it to work with `_.map`._.rest = _.tail = function(array, index, guard) {return slice.call(array, (index == null) || guard ? 1 : index);};// Trim out all falsy values from an array._.compact = function(array) {return _.filter(array, function(value){ return !!value; });};// Return a completely flattened version of an array._.flatten = function(array, shallow) {return _.reduce(array, function(memo, value) {if (_.isArray(value)) return memo.concat(shallow ? value : _.flatten(value));memo[memo.length] = value;return memo;}, []);};// Return a version of the array that does not contain the specified value(s)._.without = function(array) {return _.difference(array, slice.call(arguments, 1));};// Produce a duplicate-free version of the array. If the array has already// been sorted, you have the option of using a faster algorithm.// Aliased as `unique`._.uniq = _.unique = function(array, isSorted, iterator) {var initial = iterator ? _.map(array, iterator) : array;var result = [];_.reduce(initial, function(memo, el, i) {if (0 == i || (isSorted === true ? _.last(memo) != el : !_.include(memo, el))) {memo[memo.length] = el;result[result.length] = array[i];}return memo;}, []);return result;};// Produce an array that contains the union: each distinct element from all of// the passed-in arrays._.union = function() {return _.uniq(_.flatten(arguments, true));};// Produce an array that contains every item shared between all the// passed-in arrays. (Aliased as "intersect" for back-compat.)_.intersection = _.intersect = function(array) {var rest = slice.call(arguments, 1);return _.filter(_.uniq(array), function(item) {return _.every(rest, function(other) {return _.indexOf(other, item) >= 0;});});};// Take the difference between one array and another.// Only the elements present in just the first array will remain._.difference = function(array, other) {return _.filter(array, function(value){ return !_.include(other, value); });};// Zip together multiple lists into a single array -- elements that share// an index go together._.zip = function() {var args = slice.call(arguments);var length = _.max(_.pluck(args, 'length'));var results = new Array(length);for (var i = 0; i < length; i++) results[i] = _.pluck(args, "" + i);return results;};// If the browser doesn't supply us with indexOf (I'm looking at you, **MSIE**),// we need this function. Return the position of the first occurrence of an// item in an array, or -1 if the item is not included in the array.// Delegates to **ECMAScript 5**'s native `indexOf` if available.// If the array is large and already in sort order, pass `true`// for **isSorted** to use binary search._.indexOf = function(array, item, isSorted) {if (array == null) return -1;var i, l;if (isSorted) {i = _.sortedIndex(array, item);return array[i] === item ? i : -1;}if (nativeIndexOf && array.indexOf === nativeIndexOf) return array.indexOf(item);for (i = 0, l = array.length; i < l; i++) if (array[i] === item) return i;return -1;};// Delegates to **ECMAScript 5**'s native `lastIndexOf` if available._.lastIndexOf = function(array, item) {if (array == null) return -1;if (nativeLastIndexOf && array.lastIndexOf === nativeLastIndexOf) return array.lastIndexOf(item);var i = array.length;while (i--) if (array[i] === item) return i;return -1;};// Generate an integer Array containing an arithmetic progression. A port of// the native Python `range()` function. See// [the Python documentation](http://docs.python.org/library/functions.html#range)._.range = function(start, stop, step) {if (arguments.length <= 1) {stop = start || 0;start = 0;}step = arguments[2] || 1;var len = Math.max(Math.ceil((stop - start) / step), 0);var idx = 0;var range = new Array(len);while(idx < len) {range[idx++] = start;start += step;}return range;};