Created nonzero.md

content/numpy/concepts/built-in-functions/terms/nonzero/nonzero.md

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+---
+Title: '.nonzero()'
+Description: 'Returns the indices of the nonzero elements in a given array.'
+Subjects:
+  - 'Computer Science'
+  - 'Data Science'
+Tags:
+  - 'Arrays'
+  - 'Functions'
+  - 'NumPy'
+CatalogContent:
+  - 'learn-python-3'
+  - 'paths/computer-science'
+---
+
+The **`.nonzero()`** function function identifies and returns the indices of the non-zero elements in a NumPy array. The `.nonzero()` function is commonly used in data preprocessing and analysis to filter out or extract meaningful, non-zero elements from datasets. It is also valuable in sparse matrix operations and machine learning workflows, where zero values often represent missing, default, or irrelevant data that needs to be handled separately.
+
+## Syntax
+
+```psuedo
+numpy.nonzero(a)
+```
+
+**Parameters:**
+
+- `a`: The input array.
+
+**Return value:**
+
+The `.nonzero()` function returns a tuple of arrays. There's one array for each dimension of the input array.
+
+## Example 1: Using `.nonzero()` with a 1D Array
+
+The following demonstrates how to find the nonzero indices of a one-dimensional NumPy array and print the array of the nonzero values:
+
+```py
+import numpy as np
+
+# Create a 1D array
+array1 = np.array([0, 1, 0, 2, 3, 0, 0, 4, 0, 5])
+
+# Compute the indices of the nonzero values and then the array of the nonzero values
+nonzero_indices = np.nonzero(array1)
+no_zero_array1 = array1[nonzero_indices]
+
+print("Array:", array1)
+print("Nonzero Indices:", nonzero_indices)
+print("Nonzero Values:", no_zero_array1)
+```
+
+This example results in the following output:
+
+```shell
+Array: [0 1 0 2 3 0 0 4 0 5]
+Nonzero Indices: (array([1, 3, 4, 7, 9]),)
+Nonzero Values: array([1, 2, 3, 4, 5])
+```
+
+## Example 2: Using `.nonzero()` with a 2D Array
+
+The following demonstrates how to find the nonzero indices of a two-dimensional NumPy array and print the array of the nonzero values:
+
+```py
+import numpy as np
+
+# Create a 2D array
+array2 = np.array([[1, 2], [0, 3]])
+
+# Compute the indices of the nonzero values and then the array without the zeros
+nonzero_indices = np.nonzero(array2)
+no_zero_array2 = array2[nonzero_indices]
+
+print("Array:", array2)
+print("Nonzero Indices:", nonzero_indices)
+print("Nonzero Values:", no_zero_array2)
+```
+
+This example results in the following output:
+
+```shell
+Array: [[1 2]
+       [0 3]]
+Nonzero Indices: (array([0, 0, 1]), array([0, 1, 1]))
+Nonzero Values: [1, 2, 3]
+```