Array of arrays (jagged arrays) are faster than multi-dimensional arrays and can be used more effectively. Multidimensional arrays have nicer syntax. If you write some simple code using jagged and multidimensional arrays and then inspect the compiled assembly with an IL disassembler you will see that the storage and retrieval from jagged (or single dimensional) … Read more
One is an array of arrays, and one is a 2d array. The former can be jagged, the latter is uniform. That is, a double[][] can validly be: double[][] x = new double[5][]; x[0] = new double[10]; x[1] = new double[5]; x[2] = new double[3]; x[3] = new double[100]; x[4] = new double[1]; Because each … Read more
Arrays on the type level An array type is denoted as T[n] where T is the element type and n is a positive size, the number of elements in the array. The array type is a product type of the element type and the size. If one or both of those ingredients differ, you get … Read more
You’ve got a workable idea, but the #flatten! is in the wrong place — it flattens its receiver, so you could use it to turn [1, 2, [‘foo’, ‘bar’]] into [1,2,’foo’,’bar’]. I’m doubtless forgetting some approaches, but you can concatenate: a1.concat a2 a1 + a2 # creates a new array, as does a1 += a2 … Read more
You are right, the function you’re looking for is array_multisort(). Here’s an example taken straight from the manual and adapted to your case: $price = array(); foreach ($inventory as $key => $row) { $price[$key] = $row[‘price’]; } array_multisort($price, SORT_DESC, $inventory); As of PHP 5.5.0 you can use array_column() instead of that foreach: $price = array_column($inventory, … Read more
Using numpy.unique: import numpy a = numpy.array([0, 3, 0, 1, 0, 1, 2, 1, 0, 0, 0, 0, 1, 3, 4]) unique, counts = numpy.unique(a, return_counts=True) >>> dict(zip(unique, counts)) {0: 7, 1: 4, 2: 1, 3: 2, 4: 1} Non-numpy method using collections.Counter; import collections, numpy a = numpy.array([0, 3, 0, 1, 0, 1, 2, … Read more
If your row length is a compile time constant, C++11 allows auto arr2d = new int [nrows][CONSTANT]; See this answer. Compilers like gcc that allow variable-length arrays as an extension to C++ can use new as shown here to get fully runtime-variable array dimension functionality like C99 allows, but portable ISO C++ is limited to … Read more
Use usort, here’s an example adapted from the manual: function cmp($a, $b) { return strcmp($a->name, $b->name); } usort($your_data, “cmp”); You can also use any callable as the second argument. Here are some examples: Using anonymous functions (from PHP 5.3) usort($your_data, function($a, $b) {return strcmp($a->name, $b->name);}); From inside a class usort($your_data, array($this, “cmp”)); // “cmp” should … Read more
You’re technically trying to index an uninitialized array. You have to first initialize the outer list with lists before adding items; Python calls this “list comprehension”. # Creates a list containing 5 lists, each of 8 items, all set to 0 w, h = 8, 5 Matrix = [[0 for x in range(w)] for y … Read more
var items = [ [1, 2], [3, 4], [5, 6] ]; console.log(items[0][0]); // 1 console.log(items[0][1]); // 2 console.log(items[1][0]); // 3 console.log(items[1][1]); // 4 console.log(items);