np.argsort() for sort indices in NumPy - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does np.argsort() do in NumPy?

np.argsort() returns the indices that would sort an array. It tells you the order to arrange elements to get a sorted array.

beginner

How can you use np.argsort() to sort an array?

Use the indices from np.argsort() to reorder the original array. For example, arr[np.argsort(arr)] gives the sorted array.

beginner

What is the difference between np.sort() and np.argsort()?

np.sort() returns the sorted array itself, while np.argsort() returns the indices that would sort the array.

intermediate

Can np.argsort() be used on multi-dimensional arrays?

Yes, by specifying the axis parameter, np.argsort() returns indices that sort along that axis.

intermediate

Why might you want to use np.argsort() instead of sorting the array directly?

Using np.argsort() lets you keep track of the original positions of elements after sorting, useful for reordering related data or preserving index relationships.

What does np.argsort([3, 1, 2]) return?

A [0, 1, 2]

B [1, 2, 0]

C [2, 1, 0]

D [1, 0, 2]

The sorted array is [1, 2, 3]. The indices to get this order from the original array are [1, 2, 0].

Which function returns the sorted array itself?

A np.order()

B np.argsort()

C np.indexsort()

D np.sort()

np.sort() returns the sorted array. np.argsort() returns indices.

How do you get a sorted array from np.argsort() indices?

A Multiply the array by the indices

B Add the indices to the array

C Use the indices to reorder the original array

D Sort the indices again

Use the indices to reorder the original array: arr[np.argsort(arr)].

What parameter lets you sort along a specific axis in np.argsort()?

A axis

B order

C direction

D sort_axis

The axis parameter specifies which axis to sort along in multi-dimensional arrays.

Why is np.argsort() useful when working with related data arrays?

A It gives indices to reorder related arrays consistently

B It removes duplicates

C It changes the data type

D It sorts all arrays automatically

np.argsort() provides indices to reorder related arrays in the same sorted order.

Explain how np.argsort() works and how you can use it to sort an array.

Think about how indices tell you the order of elements.

Describe a situation where using np.argsort() is better than directly sorting the array.

Imagine you have two lists that must stay aligned after sorting.