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Created .ones() entry for Python Numpy (#6898)
* Created .ones() entry for Python Numpy * Update ones.md * Update ones.md * added a codebyte example, formatted the parameters, fixed format issues * Update ones.md * fixed format * Update ones.md * Update ones.md * Format ---------
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---
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Title: '.ones()'
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Description: 'Creates a new array of the given shape and type, filled with ones.'
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Subjects:
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- 'Computer Science'
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- 'Data Science'
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Tags:
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- 'Arrays'
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- 'Functions'
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- 'Linear Algebra'
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- 'NumPy'
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CatalogContent:
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- 'learn-python-3'
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- 'paths/data-science'
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---
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In NumPy, the **`.ones()`** function creates a new array of the given shape and type, filled with ones.
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This function is particularly useful when there is a need to initialize an array with a placeholder value of `1`, which might be multiplied by another value or used in various numerical computations later.
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## Syntax
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```pseudo
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numpy.ones(shape, dtype=None, order='C', *, like=None)
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```
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**Parameters:**
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- `shape` (`int` or tuple of `int`): Defines the dimensions of the new array.
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- If an int, a 1-D array of that length is created.
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- If a tuple of ints, an array with those dimensions is created (e.g., (2, 3) for a 2x3 array).
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- `dtype` (optional): The desired data type for the array elements. Defaults to `float64`. Examples: `int32`, `bool_`, `float`.
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- `order`: ({'C', 'F'}, optional): Controls whether the array is stored in row-major or column-major memory layout.
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- `'C'` (default): Row-major (C-style)
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- `'F'`: Column-major (Fortran-style)
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- `like`(array_like, optional): Reference object for creating arrays not strictly of NumPy type. If `None`, a NumPy array is returned.
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**Return value:**
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- `out` (ndarray): An array of ones of the given shape, `dtype`, and order.
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## Example
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This example demonstrates the usage of the `.ones()` function:
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```py
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import numpy as np
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# Create a 1-D array with 5 ones (default dtype is float64)
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arr1 = np.ones(5)
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print("Array 1:\n", arr1)
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print("Data type of Array 1:", arr1.dtype)
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print("Shape of Array 1:", arr1.shape)
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# Create a 2-D array (3 rows, 4 columns) of ones with integer type
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arr2 = np.ones((3, 4), dtype=int)
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print("\nArray 2:\n", arr2)
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print("Data type of Array 2:", arr2.dtype)
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print("Shape of Array 2:", arr2.shape)
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# Create a 3-D array of ones
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arr3 = np.ones((2, 3, 2))
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print("\nArray 3:\n", arr3)
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print("Data type of Array 3:", arr3.dtype)
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print("Shape of Array 3:", arr3.shape)
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```
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Here is the output:
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```shell
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Array 1:
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[1. 1. 1. 1. 1.]
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Data type of Array 1: float64
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Shape of Array 1: (5,)
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Array 2:
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[[1 1 1 1]
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[1 1 1 1]
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[1 1 1 1]]
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Data type of Array 2: int64
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Shape of Array 2: (3, 4)
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Array 3:
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[[[1. 1.]
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[1. 1.]
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[1. 1.]]
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[[1. 1.]
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[1. 1.]
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[1. 1.]]]
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Data type of Array 3: float64
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Shape of Array 3: (2, 3, 2)
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```
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## Codebyte Example: Add Bias Term to a Feature Matrix in Machine Learning
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In many machine learning algorithms (like linear regression), there is a need to add a bias column of 1s to the input feature matrix. Here's how `numpy.ones()` can be used:
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```codebyte/python
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import numpy as np
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# Feature matrix (e.g., 4 samples with 3 features each)
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X = np.array([
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[5.1, 3.5, 1.4],
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[4.9, 3.0, 1.4],
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[6.2, 3.4, 5.4],
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[5.9, 3.0, 5.1]
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])
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# Create a column of ones for the bias term
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bias = np.ones((X.shape[0], 1))
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# Concatenate bias and features
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X_with_bias = np.hstack((bias, X))
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print("Feature Matrix with Bias Term:\n", X_with_bias)
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```

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