Array Manipulation

Reference for shape manipulation, stacking, splitting, and array transformation operations.

reshape()

Reshape the array to a new shape.

php

public function reshape(array $newShape, string $order = 'C'): NDArray

Returns a new array with the specified shape. Supports both C-order (row-major, order='C') and F-order (column-major, order='F').

Parameters

Name	Type	Description
`$newShape`	`array<int>`	New shape
`$order`	`string`	Memory layout: 'C' for row-major, 'F' for column-major. Default: `'C'`

Returns

NDArray - Reshaped array. This will be a new view object if the array is contiguous; otherwise, it will be a copy. Note there is no guarantee of the memory layout (C- or Fortran- contiguous) of the returned array.

Examples

php

$arr = NDArray::arange(12);

// Reshape to 2D
$matrix = $arr->reshape([3, 4]);
print_r($matrix->shape());
// Output: [3, 4]

// Reshape to 3D
$tensor = $arr->reshape([2, 2, 3]);
print_r($tensor->shape());
// Output: [2, 2, 3]

transpose()

Transpose the array.

php

public function transpose(): NDArray

For 2D arrays, swaps rows and columns. For nD arrays, reverses the order of all axes.

Parameters

None.

Returns

NDArray - A view of the array with its axes permuted. A view is returned whenever the array is contiguous; otherwise a copy is made.

Examples

php

$matrix = NDArray::array([
    [1, 2, 3],
    [4, 5, 6]
]);

$transposed = $matrix->transpose();
print_r($transposed->shape());
// Output: [3, 2]

print_r($transposed->toArray());
// Output: [[1, 4], [2, 5], [3, 6]]

flatten()

Flatten the array to 1D.

php

public function flatten(): NDArray

Always returns a copy in C-order (row-major).

Parameters

None.

Returns

NDArray - Flattened 1D array (copy).

Examples

php

$matrix = NDArray::array([[1, 2], [3, 4]]);

$flat = $matrix->flatten();
print_r($flat->toArray());
// Output: [1, 2, 3, 4]

ravel()

Ravel the array to 1D.

php

public function ravel(string $order = 'C'): NDArray

Similar to flatten() but may return a view if the array is contiguous.

Parameters

Name	Type	Description
`$order`	`string`	Memory layout: 'C' for row-major, 'F' for column-major. Default: `'C'`

Returns

NDArray - A 1D view of the array if it is contiguous; otherwise, a contiguous 1D copy.

Examples

php

$matrix = NDArray::array([[1, 2], [3, 4]]);

$raveled = $matrix->ravel();
print_r($raveled->toArray());
// Output: [1, 2, 3, 4]

Flattening Comparison

When you need a one-dimensional representation of an array, you have three options:

Method	Returns	When to Use
`flatten()`	1D NDArray (copy)	When you need a real array and want to ensure no shared memory
`ravel()`	1D NDArray (view or copy)	When you need a real array and want zero-copy when possible
`flat()`	FlatIterator	When you just need to iterate or index elements, not a full array

Key Differences:

flatten() always creates a new contiguous copy. Changes to the result don't affect the original, and vice versa. This is safest when you need independence.

ravel() returns a view if the array is already contiguous, avoiding a copy. For non-contiguous arrays (like slices or transposed arrays), it falls back to copying. Use this when performance matters and you can handle either views or copies.

flat() returns an iterator, not an array. It provides element-by-element access without copying any data, working efficiently even on complex views. However, you get an iterator object, not an NDArray, so you can't use array methods like mean() or sum() on it directly.

php

$matrix = NDArray::array([[1, 2], [3, 4]]);

// Get a 1D array (copy)
$copy = $matrix->flatten();
echo $copy->sum();  // Works: 10

// Get a 1D array (view if contiguous)
$view = $matrix->ravel();
echo $view->mean();  // Works: 2.5

// Iterate without copying
foreach ($matrix->flat() as $value) {
    echo $value . " ";
}
// Output: 1 2 3 4

swapaxes()

Swap two axes of the array.

php

public function swapaxes(int $axis1, int $axis2): NDArray

Parameters

Name	Type	Description
`$axis1`	`int`	First axis to swap
`$axis2`	`int`	Second axis to swap

Returns

NDArray - Array with swapped axes (view).

Examples

php

$tensor = NDArray::arange(24)->reshape([2, 3, 4]);

$result = $tensor->swapaxes(0, 2);
print_r($result->shape());
// Output: [4, 3, 2]

permute()

Permute axes of the array.

php

public function permute(int ...$axes): NDArray

Reorders the axes according to the given permutation. For example, permute(1, 0) on a 2D array is equivalent to transpose().

Parameters

Name	Type	Description
`$axes`	`int...`	New order of axes (variadic)

Returns

NDArray - Array with permuted axes (view).

Examples

php

$tensor = NDArray::ones([2, 3, 4, 5]);

$permuted = $tensor->permute(2, 0, 3, 1);
print_r($permuted->shape());
// Output: [4, 2, 5, 3]

mergeaxes()

Merge axes by combining one axis into another.

php

public function mergeaxes(int $take, int $into): NDArray

Merges the axis take into axis into by combining their dimensions. The take axis is removed and its size is multiplied into the into axis.

Parameters

Name	Type	Description
`$take`	`int`	Axis to merge from (will be removed)
`$into`	`int`	Axis to merge into (size will be multiplied)

Returns

NDArray - A view of the array with merged axes. This is always a view into the original array with updated shape and strides.

Examples

php

$tensor = NDArray::arange(24)->reshape([2, 3, 4]);

$result = $tensor->mergeaxes(1, 0);
print_r($result->shape());
// Output: [6, 4]

flip()

Reverse the order of elements in an array along the given axis or axes.

php

public function flip(array|int|null $axes = null): NDArray

Parameters

Name	Type	Description
`$axes`	`array<int>\|int\|null`	Axis or axes to flip. If null, flip over all axes.

Returns

NDArray - Array with reversed elements.

Examples

php

$arr = NDArray::array([[1, 2, 3], [4, 5, 6]]);

// Flip single axis
$result = $arr->flip(0);
print_r($result->toArray());
// Output: [[4, 5, 6], [1, 2, 3]]

// Flip with negative index
$result = $arr->flip(-1);
print_r($result->toArray());
// Output: [[3, 2, 1], [6, 5, 4]]

// Flip multiple axes
$result = $arr->flip([0, 1]);
print_r($result->toArray());
// Output: [[6, 5, 4], [3, 2, 1]]

// Flip all axes
$result = $arr->flip();
print_r($result->toArray());
// Output: [[6, 5, 4], [3, 2, 1]]

insertaxis()

Insert a new axis at the specified position.

php

public function insertaxis(int $axis): NDArray

The new axis always has length 1.

Parameters

Name	Type	Description
`$axis`	`int`	Position where new axis is inserted

Returns

NDArray - Array with new axis (view).

Examples

php

$arr = NDArray::array([1, 2, 3]);

$expanded = $arr->insertaxis(0);
print_r($expanded->shape());
// Output: [1, 3]

$expanded = $arr->insertaxis(1);
print_r($expanded->shape());
// Output: [3, 1]

expandDims()

Expand dimensions by inserting a new axis.

php

public function expandDims(int $axis): NDArray

Alias for insertaxis().

Parameters

Name	Type	Description
`$axis`	`int`	Position where new axis is inserted

Returns

NDArray - A view of the array with the number of dimensions increased by inserting a new axis of length 1. This is always a view into the original array.

Examples

php

$arr = NDArray::array([1, 2, 3]);

$expanded = $arr->expandDims(0);
print_r($expanded->shape());
// Output: [1, 3]

squeeze()

Remove axes of length 1 from the array.

php

public function squeeze(?array $axes = null): NDArray

If no axes are specified, removes all length-1 axes.

Parameters

Name	Type	Description
`$axes`	`array<int>\|null`	Specific axes to squeeze (null for all). Default: `null`

Returns

NDArray - The input array, but with all or a subset of the dimensions of length 1 removed. This is always a view into the original array. Note that if all axes are squeezed, the result is a 0D array and not a scalar.

Examples

php

$arr = NDArray::ones([1, 3, 1, 4, 1]);

// Remove all single dimensions
$squeezed = $arr->squeeze();
print_r($squeezed->shape());
// Output: [3, 4]

// Remove specific axis
$squeezed = $arr->squeeze([0]);
print_r($squeezed->shape());
// Output: [3, 1, 4, 1]

pad()

Pad an array.

php

public function pad(
    array|int $padWidth,
    PadMode $mode = PadMode::Constant,
    array|bool|float|int $constantValues = 0
): NDArray

Parameters

Name	Type	Description
`$padWidth`	`array\|int`	Number of elements to pad on each side of each axis. int: same on all sides of every axis; array{int,int}: [before, after] for all axes; array per-axis: int or [before, after] per axis
`$mode`	`PadMode`	Padding mode. Default: `PadMode::Constant`
`$constantValues`	`array\|bool\|float\|int`	Constant value for PadMode::Constant. Default: `0`

Returns

NDArray - Padded array.

Examples

php

$arr = NDArray::array([[1, 2], [3, 4]]);

// Pad with zeros (1 element on each side)
$padded = $arr->pad(1);
print_r($padded->shape());
// Output: [4, 4]

// With constant value
$padded = $arr->pad(1, constantValues: 9);

tile()

Construct an array by repeating this array the number of times given by reps.

php

public function tile(array|int|NDArray $reps): NDArray

Parameters

Name	Type	Description
`$reps`	`array\|int\|NDArray`	Number of repetitions along each axis

Returns

NDArray - Tiled output array.

Examples

php

$arr = NDArray::array([[1, 2], [3, 4]]);

// Tile 2 times along axis 0 and 3 times along axis 1
$result = $arr->tile([2, 3]);
print_r($result->shape());
// Output: [4, 6]

// Tile with integer (applies to first axis only)
$result = $arr->tile(2);
print_r($result->shape());
// Output: [4, 2]

repeat()

Repeat elements of an array.

php

public function repeat(array|int|NDArray $repeats, ?int $axis = null): NDArray

Parameters

Name	Type	Description
`$repeats`	`array\|int\|NDArray`	Number of repetitions for each element
`$axis`	`int\|null`	Axis along which to repeat. Default: flattened input. Default: `null`

Returns

NDArray - Output array (same shape except along the given axis).

Examples

php

$arr = NDArray::array([1, 2, 3]);

// Repeat each element twice
$result = $arr->repeat(2);
print_r($result->toArray());
// Output: [1, 1, 2, 2, 3, 3]

// Repeat along axis
$matrix = NDArray::array([[1, 2], [3, 4]]);
$result = $matrix->repeat(2, axis: 1);
print_r($result->toArray());
// Output: [[1, 1, 2, 2], [3, 3, 4, 4]]

concatenate()

Join arrays along an existing axis.

php

public static function concatenate(array $arrays, int $axis = 0): NDArray

All arrays must have the same shape except for the dimension along the axis.

Parameters

Name	Type	Description
`$arrays`	`array<NDArray>`	Arrays to concatenate
`$axis`	`int`	Axis along which to join. Default: `0`

Returns

NDArray - Concatenated array.

Examples

php

$a = NDArray::array([[1, 2], [3, 4]]);
$b = NDArray::array([[5, 6], [7, 8]]);

$out = NDArray::concatenate([$a, $b], axis: 0);
print_r($out->shape());
// Output: [4, 2]

$out = NDArray::concatenate([$a, $b], axis: 1);
print_r($out->shape());
// Output: [2, 4]

stack()

Stack arrays along a new axis.

php

public static function stack(array $arrays, int $axis = 0): NDArray

All arrays must have identical shapes.

Parameters

Name	Type	Description
`$arrays`	`array<NDArray>`	Arrays to stack
`$axis`	`int`	Axis in the result at which the arrays are stacked. Default: `0`

Returns

NDArray - Stacked array.

Examples

php

$a = NDArray::array([1, 2, 3]);
$b = NDArray::array([4, 5, 6]);

$out = NDArray::stack([$a, $b]);
print_r($out->shape());
// Output: [2, 3]

vstack()

Stack arrays vertically (along axis 0).

php

public static function vstack(array $arrays): NDArray

Equivalent to concatenate(arrays, axis=0).

Parameters

Name	Type	Description
`$arrays`	`array<NDArray>`	Arrays to stack

Returns

NDArray - Vertically stacked array.

Examples

php

$a = NDArray::array([[1, 2], [3, 4]]);
$b = NDArray::array([[5, 6]]);

$out = NDArray::vstack([$a, $b]);
print_r($out->shape());
// Output: [3, 2]

hstack()

Stack arrays horizontally (along axis 1).

php

public static function hstack(array $arrays): NDArray

Equivalent to concatenate(arrays, axis=1).

Parameters

Name	Type	Description
`$arrays`	`array<NDArray>`	Arrays to stack

Returns

NDArray - Horizontally stacked array.

Examples

php

$a = NDArray::array([[1, 2], [3, 4]]);
$b = NDArray::array([[5], [6]]);

$out = NDArray::hstack([$a, $b]);
print_r($out->shape());
// Output: [2, 3]

split()

Split array along an axis.

php

public function split(array|int $indicesOrSections, int $axis = 0): array

If $indicesOrSections is an integer N, split into N equal parts (axis length must be divisible by N). If it is an array of indices, split at those positions.

Parameters

Name	Type	Description
`$indicesOrSections`	`array<int>\|int`	Number of equal parts, or array of split indices
`$axis`	`int`	Axis along which to split. Default: `0`

Returns

array<NDArray> - List of sub-arrays (views).

Examples

php

$arr = NDArray::arange(12)->reshape([3, 4]);

// Split into 3 equal parts along axis 0
$parts = $arr->split(3, axis: 0);
// 3 arrays of shape [1, 4]

// Split at indices
$parts = $arr->split([1, 2], axis: 1);
// 3 arrays of shape [3, 1], [3, 1], [3, 2]

vsplit()

Split array vertically (along axis 0).

php

public function vsplit(array|int $indicesOrSections): array

Parameters

Name	Type	Description
`$indicesOrSections`	`array<int>\|int`	Number of equal parts or split indices

Returns

array<NDArray> - List of sub-arrays.

Examples

php

$arr = NDArray::arange(12)->reshape([4, 3]);
$parts = $arr->vsplit(2);
// 2 arrays of shape [2, 3]

hsplit()

Split array horizontally (along axis 1).

php

public function hsplit(array|int $indicesOrSections): array

Parameters

Name	Type	Description
`$indicesOrSections`	`array<int>\|int`	Number of equal parts or split indices

Returns

array<NDArray> - List of sub-arrays.

Examples

php

$arr = NDArray::arange(12)->reshape([3, 4]);
$parts = $arr->hsplit(2);
// 2 arrays of shape [3, 2]

Summary Table

Shape Manipulation

Method	Description	Returns View?
`reshape()`	Change array shape	Sometimes
`transpose()`	Reverse axes	Yes
`flatten()`	Flatten to 1D (copy)	No
`ravel()`	Flatten to 1D (view if possible)	Sometimes
`swapaxes()`	Swap two axes	Yes
`permute()`	Reorder axes	Yes
`merge()`	Merge two axes	Yes
`flip()`	Reverse elements	No
`insertaxis()` / `expandDims()`	Add dimension	Yes
`squeeze()`	Remove length-1 dimensions	Yes
`pad()`	Pad with values	No
`tile()`	Repeat array	No
`repeat()`	Repeat elements	No

Joining and Splitting

Method	Description
`concatenate()`	Join along existing axis
`stack()`	Join along new axis
`vstack()`	Stack vertically (axis 0)
`hstack()`	Stack horizontally (axis 1)
`split()`	Split along axis
`vsplit()`	Split vertically (axis 0)
`hsplit()`	Split horizontally (axis 1)

Array Manipulation ​

reshape() ​

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transpose() ​

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flatten() ​

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ravel() ​

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Flattening Comparison ​

swapaxes() ​

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permute() ​

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mergeaxes() ​

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flip() ​

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insertaxis() ​

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expandDims() ​

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squeeze() ​

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pad() ​

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tile() ​

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repeat() ​

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concatenate() ​

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stack() ​

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vstack() ​

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hstack() ​

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split() ​

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vsplit() ​

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Array Manipulation

reshape()

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transpose()

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flatten()

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ravel()

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Flattening Comparison

swapaxes()

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permute()

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mergeaxes()

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flip()

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insertaxis()

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expandDims()

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squeeze()

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pad()

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tile()

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repeat()

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concatenate()

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stack()

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vstack()

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hstack()

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split()

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vsplit()

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