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Concatenating 1D NumPy arrays

schedule Aug 11, 2023
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We can either concatenate 1D arrays horizontally or vertically.

Concatenating horizontally

To concatenate horizontally, we can use either use the `np.concatenate(~)` or `np.hstack(~)` method.

Here's a quick example where we concatenate two 1D Numpy arrays:

``` x = np.array([1,2])y = np.array([3,4,5])z = np.concatenate([x,y]) # np.hstack([x,y]) works as wellz array([1, 2, 3, 4, 5]) ```

Since the `concatenate(~)` method takes in an array, you can easily concatenate numerous 1D arrays at once.

WARNING

Do not use + to concatenate Numpy arrays

For standard Python lists, the `+` operator can be used to concatenate lists: `[1,2] + [3,4] = [1,2,3,4]`. The + operator for Numpy arrays works entirely differently:

``` np.array([1,2]) + np.array([3,4]) array([4, 6]) ```

Concatenating vertically

To concatenate 1D Numpy arrays vertically, we can use the `np.vstack(~)` method:

``` x = np.array([1,2])y = np.array([3,4])z = np.vstack([x,y])z array([[1, 2], [3, 4]]) ```

Notice how we end up with a 2D Numpy array.

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