multidimensional-array

问题 for(int i = 0; i<100; i++) for(int j = 0; j<100; j++) array[j][i] = 0; // array[i][j] = 0; My professor said it was much more costly to initialize a two dimensional array in the first way as opposed to the second. Can someone explain what is going on underneath the hood which makes that the case? Or, do the two means of initialization have equal performance? 回答1: As @dlev mentioned, this is due to locality of reference and has to do with how the physical hardware in the computer works. Inside

问题 currently I am trying to resize a 2D Array in C using this code snippet array = (int**) realloc(array, s * 2 * sizeof(int)); Where s is the size of the array in rows and colums. However, when trying to access the new areas of the array like this, array[3][0] = x; I only get a segfault. The old areas of the array work fine. How can I solve this issue? 回答1: Assuming you declared array as int **array; and allocated as array = malloc( sizeof *array * ROWS ); if ( array ) { for ( size_t i = 0; i <

问题 currently I am trying to resize a 2D Array in C using this code snippet array = (int**) realloc(array, s * 2 * sizeof(int)); Where s is the size of the array in rows and colums. However, when trying to access the new areas of the array like this, array[3][0] = x; I only get a segfault. The old areas of the array work fine. How can I solve this issue? 回答1: Assuming you declared array as int **array; and allocated as array = malloc( sizeof *array * ROWS ); if ( array ) { for ( size_t i = 0; i <

问题 vector <int> V[] and vector< vector<int> > V both are 2D array . But what is the difference between their and where we use this in different place?? Please give a brief explanation. 回答1: vector<int> V[] is an array of vectors . vector< vector<int> > V is a vector of vectors . Using arrays are C-style coding , using vectors are C++-style coding . Quoting cplusplus.com , Vectors are sequence containers representing arrays that can change in size. Just like arrays, vectors use contiguous storage

问题 I have an array as following and I want to order that array by the value of the key "attack". First keys of the arrays (15, 13, 18) are ID of some certain item from database, so I don't want these keys to be changed when the array is sorted. Any help would be greatly appreciated. This is the array: $data = array( '15' => array( 'attack' => '45', 'defence' => '15', 'total' => '10' ), '13' => array( 'attack' => '25', 'defence' => '15', 'total' => '10' ), '18' => array( 'attack' => '35',

问题 I have two very large numpy arrays, which are both 3D. I need to find an efficient way to check if they are overlapping, because turning them both into sets first takes too long. I tried to use another solution I found here for this same problem but for 2D arrays, but I didn't manage to make it work for 3D. Here is the solution for 2D: nrows, ncols = A.shape dtype={'names':['f{}'.format(i) for i in range(ndep)], 'formats':ndep * [A.dtype]} C = np.intersect1d(A.view(dtype).view(dtype), B.view

问题 I'm trying to select the maximum value for a particular key in a multidimensional array. I'm having trouble "getting to" the key in question... So, the array (which is much more lengthy than what I'm posting here) [0] => stdClass Object ( [id] => 70 [cust] => 4 [dnum] => 1 [upper] => Array ( [0] => 66 ) ) [1] => stdClass Object ( [id] => 43 [cust] => 42 [dnum] => 2 [upper] => Array ( [0] => 77 ) ) [2] => stdClass Object ( [id] => 12 [cust] => 3 [dnum] => 0 [upper] => Array ( [0] => 99 ) ) I'm

问题 I have a multidimensional array e.g. (this can be many levels deep): $array = Array ( [21] => Array ( ) [24] => Array ( [22] => Array ( ) [25] => Array ( [26] => Array ( ) ) ) ) I am trying to loop through it to see if a certain key exists: $keySearch = 22; // key searching for function findKey($array, $keySearch) { foreach ($array as $item){ if (isset($item[$keySearch]) && false === findKey($item[$keySearch], $item)){ echo 'yes, it exists'; } } } findKey($array, $keySearch); But it finds

问题 I am trying to create a matrix transpose function for python but I can't seem to make it work. Say I have theArray = [['a','b','c'],['d','e','f'],['g','h','i']] and I want my function to come up with newArray = [['a','d','g'],['b','e','h'],['c', 'f', 'i']] So in other words, if I were to print this 2D array as columns and rows I would like the rows to turn into columns and columns into rows. I made this so far but it doesn't work def matrixTranspose(anArray): transposed = [None]*len(anArray[0

问题 I am trying to create a matrix transpose function for python but I can't seem to make it work. Say I have theArray = [['a','b','c'],['d','e','f'],['g','h','i']] and I want my function to come up with newArray = [['a','d','g'],['b','e','h'],['c', 'f', 'i']] So in other words, if I were to print this 2D array as columns and rows I would like the rows to turn into columns and columns into rows. I made this so far but it doesn't work def matrixTranspose(anArray): transposed = [None]*len(anArray[0