How to avoid selecting the same elements in a list?

Question

Assume there two lists:A=[1,2,3,4,5,6,7];B=[23,25,34,23,24,10,45]. The elements in A List represent the name of products, while those in B list represent the price of products. For example, product 1 worths 23 USD.
I want to retrieve the products whose price is 23 USD.
What I tried was shown below:

Prod_23 = []
for i in B:
  if i == 23:
    index = B.index(i)
    product = A[index]
    Prod_23.append(product)

The result was:

Prod_23 = [1,1]

But the actual result should be like:

Prod_23 = [1,4]

Could you please give me some clues of avoiding selecting the first element twice and only selecting the first and fourth elements?

Asked By: czy

||

Source

Answer 1

why don’t do this:

a[b.index(23)]

Answered By: Colonel Mustard

Answer 2

Use zip() to tie lists A and B together and use list-comprehension:

list_23 = [a for a, b in zip(A, B) if b == 23]
print(list_23)

Prints:

[1, 4]

Answered By: Andrej Kesely

Answer 3

You can also use any of the following methods for this purpose:

Python2 :

>>> indices = [A[i] for i in xrange(len(A)) if B[i] == 23]
>>> indices
[1, 4]
>>>

Python3:

Using a for-loop with `range()` ^{[Python-docs]} :

>>> indices = [A[i] for i in range(len(A)) if B[i] == 23] # or [A[i] for i in A if B[i] == 23]
>>> indices
[1, 4]
>>>

Using for-loop and `enumerate()` ^{[Python-docs]} :

>>> indices = [A[i] for i, x in enumerate(B) if x == 23]
>>> indices
[1, 4]
>>>

Using `locate()` ^{[more-itertools-docs]} with for-loop:

>>> from more_itertools import locate
>>> indices = [A[i] for i in locate(B, lambda x: x == 23)]
>>> indices
[1, 4]
>>>

Using `locate()` ^{[more-itertools-docs]} with `itemgetter()` ^{[Python-docs]}

>>> from more_itertools import locate
>>> from operator import itemgetter
>>> indices = list(itemgetter(*locate(B, lambda x: x == 23))(A))
>>> indices
[1, 4]
>>>

Answered By: Javad

How to avoid selecting the same elements in a list?

Question:

Answers:

Python2 :

Python3:

Using a for-loop with `range()` ^{[Python-docs]} :

Using for-loop and `enumerate()` ^{[Python-docs]} :

Using `locate()` ^{[more-itertools-docs]} with for-loop:

Using `locate()` ^{[more-itertools-docs]} with `itemgetter()` ^{[Python-docs]}

How to avoid selecting the same elements in a list?

Question:

Answers:

Python2 :

Python3:

Using a for-loop with range() [Python-docs] :

Using for-loop and enumerate() [Python-docs] :

Using locate() [more-itertools-docs] with for-loop:

Using locate() [more-itertools-docs] with itemgetter() [Python-docs]

Using a for-loop with `range()` ^{[Python-docs]} :

Using for-loop and `enumerate()` ^{[Python-docs]} :

Using `locate()` ^{[more-itertools-docs]} with for-loop:

Using `locate()` ^{[more-itertools-docs]} with `itemgetter()` ^{[Python-docs]}