How to Find the First Index of an Element in a NumPy Array?

Finding the First Index of an Array Element

Similar to Python lists, NumPy arrays offer a method for locating the first occurrence of a specific value. This question delves into the NumPy equivalent of the list.index() method.

NumPy's Index Retrieval Method

To retrieve the index of the first element in a NumPy array that matches a given value, utilize the np.where function:

itemindex = np.where(array == item)

This function returns a tuple containing two arrays:

• The first array contains the row indices of matching elements.
• The second array contains the column indices of matching elements.

This tuple provides the necessary coordinates to access the matching element within the array.

Example Usage

Consider a two-dimensional array:

array = np.array([[1, 2, 3], [4, 5, 6]])

If we want to find the first occurrence of the value 5, we can use:

itemindex = np.where(array == 5)
print(itemindex[0][0], itemindex[1][0])  # Output: 1 1

This indicates that the value 5 is located at row index 1 and column index 1 within the array, which can be confirmed by:

print(array[itemindex[0][0]][itemindex[1][0]])  # Output: 5

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