np.union1d() for union in NumPy - Step-by-Step Execution

Concept Flow - np.union1d() for union

Start with two arrays

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Find unique elements in each array

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Combine unique elements

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Sort combined elements

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Return sorted union array

np.union1d() takes two arrays, finds unique elements in each, combines them, sorts the result, and returns the sorted union.

Execution Sample

NumPy

import numpy as np
arr1 = np.array([1, 3, 5])
arr2 = np.array([3, 4, 5])
result = np.union1d(arr1, arr2)
print(result)

This code finds the sorted union of two arrays arr1 and arr2.

Execution Table

Step	Action	arr1 unique	arr2 unique	Combined	Sorted Union	Output
1	Start with arr1 and arr2	[1, 3, 5]	[3, 4, 5]
2	Find unique elements in arr1	[1, 3, 5]
3	Find unique elements in arr2		[3, 4, 5]
4	Combine unique elements			[1, 3, 5, 3, 4, 5]
5	Sort combined elements				[1, 3, 3, 4, 5, 5]
6	Remove duplicates and output					[1 3 4 5]
7	End					Execution stops

💡 All unique elements combined and sorted; duplicates removed; union returned.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	After Step 5	Final
arr1	[1, 3, 5]	[1, 3, 5]	[1, 3, 5]	[1, 3, 5]	[1, 3, 5]	[1, 3, 5]
arr2	[3, 4, 5]	[3, 4, 5]	[3, 4, 5]	[3, 4, 5]	[3, 4, 5]	[3, 4, 5]
combined				[1, 3, 5, 3, 4, 5]	[1, 3, 3, 4, 5, 5]	[1, 3, 4, 5]
result						[1 3 4 5]

Key Moments - 3 Insights

Why does the output not include duplicates like 3 and 5 twice?

np.union1d() automatically removes duplicates after combining arrays, as shown in step 6 of the execution_table where duplicates are removed before output.

Is the output always sorted?

Yes, np.union1d() sorts the combined unique elements before returning, as seen in step 5 where the combined array is sorted.

What happens if arrays have no common elements?

The function still combines and sorts all unique elements from both arrays, returning their union without duplicates, similar to the process in the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table at step 5. What is the sorted union array before duplicates are removed?

A [1, 3, 4, 5]

B [1, 3, 3, 4, 5, 5]

C [1, 3, 5]

D [3, 4, 5]

💡 Hint

Check the 'Sorted Union' column at step 5 in the execution_table.

At which step does np.union1d() remove duplicates?

A Step 6

B Step 4

C Step 5

D Step 3

💡 Hint

Look at the 'Action' column in execution_table where duplicates are removed before output.

If arr2 was [6, 7, 8], how would the final output change?

A [6 7 8]

B [1 3 4 5]

C [1 3 5 6 7 8]

D [1 3 5]

💡 Hint

Refer to variable_tracker and think how combining unique elements from arr1 and arr2 changes.

Concept Snapshot

np.union1d(arr1, arr2)
- Combines two arrays
- Finds unique elements in both
- Sorts the combined unique elements
- Returns sorted union array
- Removes duplicates automatically

Full Transcript

np.union1d() takes two arrays and finds their union. It first finds unique elements in each array, then combines them. After combining, it sorts the elements and removes duplicates. The final output is a sorted array containing all unique elements from both input arrays. For example, with arr1=[1,3,5] and arr2=[3,4,5], the union is [1,3,4,5]. This process ensures no duplicates and sorted order in the result.