|
| 1 | +--- |
| 2 | +Title: 'argmin()' |
| 3 | +Description: 'Returns the index of the minimum value in a NumPy array or along a specified axis.' |
| 4 | +Subjects: |
| 5 | + - 'Computer Science' |
| 6 | + - 'Data Science' |
| 7 | +Tags: |
| 8 | + - 'Array' |
| 9 | + - 'Data' |
| 10 | + - 'NumPy' |
| 11 | +CatalogContent: |
| 12 | + - 'learn-python-3' |
| 13 | + - 'paths/data-science' |
| 14 | +--- |
| 15 | + |
| 16 | +The **`ndarray.argmin()`** method returns the index of the minimum value in a NumPy array. The search can be performed on the flattened array or along a specified axis, and the result reflects where the smallest element appears rather than the value itself. |
| 17 | + |
| 18 | +## Syntax |
| 19 | + |
| 20 | +```pseudo |
| 21 | +ndarray.argmin(axis=None, out=None, *, keepdims=False) |
| 22 | +``` |
| 23 | + |
| 24 | +**Parameters:** |
| 25 | + |
| 26 | +- `axis` (optional): Axis along which to find the minimum index. |
| 27 | + - `None` (default): Searches the entire flattened array. |
| 28 | + - `0`: Searches column-wise |
| 29 | + - `1`: Searches row-wise |
| 30 | +- `out` (optional): Output array that receives the result. Must have the appropriate shape. |
| 31 | +- `keepdims` (optional): If `True`, the reduced axes are kept with size 1, preserving the dimension structure. |
| 32 | + |
| 33 | +**Return value:** |
| 34 | + |
| 35 | +An integer or array of integers representing the indices of the minimum values. |
| 36 | + |
| 37 | +## Example 1: Finding the Minimum Index in a 1D Array |
| 38 | + |
| 39 | +In this example, the smallest number in the array is identified, and its index is returned: |
| 40 | + |
| 41 | +```py |
| 42 | +import numpy as np |
| 43 | + |
| 44 | +arr = np.array([12, 5, 7, 3, 9]) |
| 45 | +idx = arr.argmin() |
| 46 | +print(idx) |
| 47 | +``` |
| 48 | + |
| 49 | +The output of this code is: |
| 50 | + |
| 51 | +```shell |
| 52 | +3 |
| 53 | +``` |
| 54 | + |
| 55 | +## Example 2: Finding Minimum Indices Along Rows |
| 56 | + |
| 57 | +In this example, `argmin()` is applied along `axis=1`, so each row returns the index of its smallest element: |
| 58 | + |
| 59 | +```py |
| 60 | +import numpy as np |
| 61 | + |
| 62 | +arr = np.array([[4, 9, 1], |
| 63 | + [8, 3, 6]]) |
| 64 | + |
| 65 | +idx = arr.argmin(axis=1) |
| 66 | +print(idx) |
| 67 | +``` |
| 68 | + |
| 69 | +The output of this code is: |
| 70 | + |
| 71 | +```shell |
| 72 | +[2 1] |
| 73 | +``` |
| 74 | + |
| 75 | +## Codebyte Example |
| 76 | + |
| 77 | +In this example, the minimum index is found both in the flattened array and along each column to show how the output changes with the `axis` parameter: |
| 78 | + |
| 79 | +```codebyte/python |
| 80 | +import numpy as np |
| 81 | +
|
| 82 | +arr = np.array([[15, 7, 9], |
| 83 | + [2, 11, 5], |
| 84 | + [6, 4, 8]]) |
| 85 | +
|
| 86 | +flat_index = arr.argmin() |
| 87 | +col_indices = arr.argmin(axis=0) |
| 88 | +
|
| 89 | +print("Index of minimum in flattened array:", flat_index) |
| 90 | +print("Index of minimum in each column:", col_indices) |
| 91 | +``` |
| 92 | + |
| 93 | +## Frequently Asked Questions |
| 94 | + |
| 95 | +### 1. What does NumPy `argmin()` do? |
| 96 | + |
| 97 | +NumPy's `argmin()` returns the index location of the smallest element inside an array. Instead of giving the minimum value, it identifies where that value appears, which is essential for position-based analysis. |
| 98 | + |
| 99 | +### 2. What is the difference between `argmin()` and `nanargmin()`? |
| 100 | + |
| 101 | +`argmin()` considers all values, including NaNs, while `nanargmin()` ignores NaNs and returns the index of the smallest non-NaN value. |
| 102 | + |
| 103 | +### 3. What is the difference between `argmin()` and `min()` in Python? |
| 104 | + |
| 105 | +`min()` (or `ndarray.min()`) returns the smallest value itself, while `argmin()` returns the index where that value occurs. One answers “what is the smallest value”, and the other answers “where is that smallest value located”. |
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