Statistics

Reference for statistical reduction operations.

These methods aggregate array values to compute statistical measures like sum, mean, variance, and standard deviation.

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sum()

public function sum(?int $axis = null, bool $keepdims = false): float|int|NDArray

Sum of array elements over a given axis.

Parameters

Parameter	Type	Description
$axis	int|null	Axis along which to sum. If null, sum over all elements. Optional. Default: null.
$keepdims	bool	If true, the reduced axis is retained with size 1. Optional. Default: false.

Returns

• float|int|NDArray - Scalar if axis is null, otherwise an NDArray.

Examples

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

// Sum all elements
$total = $arr->sum();
echo $total;
// Output: 21

// Sum along axis 0 (columns)
$col_sums = $arr->sum(axis: 0);
print_r($col_sums->toArray());
// Output: [5, 7, 9]

// Sum along axis 1 (rows)
$row_sums = $arr->sum(axis: 1);
print_r($row_sums->toArray());
// Output: [6, 15]

// Keep dimensions
$sums = $arr->sum(axis: 1, keepdims: true);
print_r($sums->shape());
// Output: [2, 1]

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mean()

public function mean(?int $axis = null, bool $keepdims = false): float|NDArray

Mean of array elements over a given axis.

Parameters

Parameter	Type	Description
$axis	int|null	Axis along which to compute mean. If null, compute mean of all elements. Optional. Default: null.
$keepdims	bool	If true, the reduced axis is retained with size 1. Optional. Default: false.

Returns

• float|NDArray - Scalar if axis is null, otherwise an NDArray.

Examples

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

echo $arr->mean();
// Output: 3.5

$row_means = $arr->mean(axis: 1);
print_r($row_means->toArray());
// Output: [2.0, 5.0]

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var()

public function var(?int $axis = null, int $ddof = 0, bool $keepdims = false): float|NDArray

Variance of array elements over a given axis.

Parameters

Parameter	Type	Description
$axis	int|null	Axis along which to compute variance. If null, compute variance of all elements. Optional. Default: null.
$ddof	int	Delta degrees of freedom (0 for population, 1 for sample). Optional. Default: 0.
$keepdims	bool	If true, the reduced axis is retained with size 1. Optional. Default: false.

Returns

• float|NDArray - Scalar if axis is null, otherwise an NDArray.

Examples

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

echo $arr->var();
// Output: 2.0 (population variance)

echo $arr->var(ddof: 1);
// Output: 2.5 (sample variance)

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std()

public function std(?int $axis = null, int $ddof = 0, bool $keepdims = false): float|NDArray

Standard deviation of array elements over a given axis.

Parameters

Parameter	Type	Description
$axis	int|null	Axis along which to compute std. If null, compute std of all elements. Optional. Default: null.
$ddof	int	Delta degrees of freedom (0 for population, 1 for sample). Optional. Default: 0.
$keepdims	bool	If true, the reduced axis is retained with size 1. Optional. Default: false.

Returns

• float|NDArray - Scalar if axis is null, otherwise an NDArray.

Examples

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

echo $arr->std();
// Output: 1.414... (population std)

echo $arr->std(ddof: 1);
// Output: 1.581... (sample std)

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min()

public function min(?int $axis = null, bool $keepdims = false): float|int|NDArray

Minimum of array elements over a given axis.

Parameters

Parameter	Type	Description
$axis	int|null	Axis along which to find minimum. If null, find minimum of all elements. Optional. Default: null.
$keepdims	bool	If true, the reduced axis is retained with size 1. Optional. Default: false.

Returns

• float|int|NDArray - Scalar if axis is null, otherwise an NDArray.

Examples

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

echo $arr->min();
// Output: 1

$col_mins = $arr->min(axis: 0);
print_r($col_mins->toArray());
// Output: [1, 2, 3]

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max()

public function max(?int $axis = null, bool $keepdims = false): float|int|NDArray

Maximum of array elements over a given axis.

Parameters

Parameter	Type	Description
$axis	int|null	Axis along which to find maximum. If null, find maximum of all elements. Optional. Default: null.
$keepdims	bool	If true, the reduced axis is retained with size 1. Optional. Default: false.

Returns

• float|int|NDArray - Scalar if axis is null, otherwise an NDArray.

Examples

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

echo $arr->max();
// Output: 6

$col_maxs = $arr->max(axis: 0);
print_r($col_maxs->toArray());
// Output: [4, 5, 6]

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product()

public function product(?int $axis = null, bool $keepdims = false): float|int|NDArray

Product of array elements over a given axis.

Parameters

Parameter	Type	Description
$axis	int|null	Axis along which to compute product. If null, compute product of all elements. Optional. Default: null.
$keepdims	bool	If true, the reduced axis is retained with size 1. Optional. Default: false.

Returns

• float|int|NDArray - Scalar if axis is null, otherwise an NDArray.

Examples

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

echo $arr->product();
// Output: 720

$row_prods = $arr->product(axis: 1);
print_r($row_prods->toArray());
// Output: [6, 120]

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any()

Test whether any element is true over a given axis.

public function any(?int $axis = null, bool $keepdims = false): bool|NDArray

For non-bool arrays, zero is treated as false and non-zero as true. For complex numbers, the value is false if both real and imag parts are zero.

Parameters

Parameter	Type	Description
$axis	int|null	Axis along which to check. If null, checks the entire array. Optional. Default: null.
$keepdims	bool	If true, the reduced axis is retained with size 1. Optional. Default: false.

Returns

• bool|NDArray - Scalar boolean if axis is null, otherwise an NDArray of bool.

Examples

$arr = NDArray::array([[0, 0], [0, 5]]);

// Check all elements
$result = $arr->any();
echo $result ? 'true' : 'false';  // true

// Check along axis 0 (columns)
$col_result = $arr->any(axis: 0);
print_r($col_result->toArray());  // [false, true]

// Check along axis 1 (rows)
$row_result = $arr->any(axis: 1);
print_r($row_result->toArray());  // [false, true]

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all()

Test whether all elements are true over a given axis.

public function all(?int $axis = null, bool $keepdims = false): bool|NDArray

For non-bool arrays, zero is treated as false and non-zero as true. For complex numbers, the value is false if both real and imag parts are zero.

Parameters

Parameter	Type	Description
$axis	int|null	Axis along which to check. If null, checks the entire array. Optional. Default: null.
$keepdims	bool	If true, the reduced axis is retained with size 1. Optional. Default: false.

Returns

• bool|NDArray - Scalar boolean if axis is null, otherwise an NDArray of bool.

Examples

$arr = NDArray::array([[1, 1], [1, 0]]);

// Check all elements
$result = $arr->all();
echo $result ? 'true' : 'false';  // false

// Check along axis 0 (columns)
$col_result = $arr->all(axis: 0);
print_r($col_result->toArray());  // [true, false]

// Check along axis 1 (rows)
$row_result = $arr->all(axis: 1);
print_r($row_result->toArray());  // [true, false]

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Summary Table

Method	Description	Returns
sum()	Sum of elements	Scalar or array
mean()	Arithmetic mean	Scalar or array
var()	Variance	Scalar or array
std()	Standard deviation	Scalar or array
min()	Minimum value	Scalar or array
max()	Maximum value	Scalar or array
product()	Product of elements	Scalar or array
any()	Any element true	Scalar or array
all()	All elements true	Scalar or array

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