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Accessing a value in a 2D arrayAccessing columns of a 2D arrayAccessing rows of a 2D arrayCalculating the determinant of a matrixChecking allowed values for a NumPy data typeChecking if a NumPy array is a view or copyChecking the version of NumPyChecking whether a NumPy array contains a given rowComputing Euclidean distance using NumpyConcatenating 1D arraysConverting array to lowercaseConverting type of NumPy array to stringCreating a copy of an arrayDifference between Python List and Numpy arrayDifference between the methods array_equal and array_equivDifference between the methods mod and fmodDifference between the methods power and float_powerFinding the closest value in an arrayFinding the Index of Largest Value in a Numpy ArrayFinding the Index of Smallest Value in a Numpy ArrayFinding the most frequent value in a NumPy arrayFlattening Numpy arraysGetting constant PiGetting elements from a two dimensional array using two dimensional array of indicesGetting indices of N maximum valuesGetting indices of N minimum valuesGetting the number of columns of a 2D arrayGetting the number of non-zero elements in a NumPy arrayGetting the number of rows of a 2D arrayInitializing an array of onesInitializing an array of zerosInitializing an identity matrixLimiting array values to a certain rangePerforming linear regressionPrinting full or truncated NumPy arrayPrinting large Numpy arrays without truncationRemoving rows containing NaN in a NumPy arrayReversing a NumPy arraySaving NumPy array to a fileShape of Numpy ArraysSorting value of one array according to anotherSuppressing scientific notation
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Concatenating 1D NumPy arrays

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schedule Mar 10, 2022
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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 well
z
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])

Notice how instead of a concatenation, we got an element-wise addition.

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.

robocat
Published by Isshin Inada
Edited by 0 others
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