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* @license Apache-2.0
*
* Copyright (c) 2023 The Stdlib Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
'use strict';
// MAIN //
/**
* Flattens a four-dimensional nested array.
*
* ## Notes
*
* - The function assumes that all nested arrays have the same length (i.e., the input array is **not** a ragged array).
*
* @param {Array<Array<Array<Collection>>>} x - input nested array
* @param {NonNegativeIntegerArray} shape - array shape
* @param {boolean} colexicographic - specifies whether to flatten array values in colexicographic order
* @returns {Array} flattened array
*
* @example
* var x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
*
* var out = flatten4d( x, [ 2, 1, 1, 2 ], false );
* // returns [ 1, 2, 3, 4 ]
*
* @example
* var x = [ [ [ [ 1, 2 ] ] ], [ [ [ 3, 4 ] ] ] ];
*
* var out = flatten4d( x, [ 2, 1, 1, 2 ], true );
* // returns [ 1, 3, 2, 4 ]
*/
function flatten4d( x, shape, colexicographic ) {
var out;
var S0;
var S1;
var S2;
var S3;
var i0;
var i1;
var i2;
var i3;
var a0;
var a1;
var a2;
// Extract loop variables:
S0 = shape[ 3 ]; // for nested arrays, the last dimensions have the fastest changing indices
S1 = shape[ 2 ];
S2 = shape[ 1 ];
S3 = shape[ 0 ];
// Initialize an output array:
out = [];
// Iterate over the array dimensions...
if ( colexicographic ) {
for ( i0 = 0; i0 < S0; i0++ ) {
for ( i1 = 0; i1 < S1; i1++ ) {
for ( i2 = 0; i2 < S2; i2++ ) {
for ( i3 = 0; i3 < S3; i3++ ) {
out.push( x[ i3 ][ i2 ][ i1 ][ i0 ] ); // equivalent to storing in column-major (Fortran-style) order
}
}
}
}
return out;
}
for ( i3 = 0; i3 < S3; i3++ ) {
a2 = x[ i3 ];
for ( i2 = 0; i2 < S2; i2++ ) {
a1 = a2[ i2 ];
for ( i1 = 0; i1 < S1; i1++ ) {
a0 = a1[ i1 ];
for ( i0 = 0; i0 < S0; i0++ ) {
out.push( a0[ i0 ] ); // equivalent to storing in row-major (C-style) order
}
}
}
}
return out;
}
// EXPORTS //
module.exports = flatten4d;
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