CODEWITHSUNDEEP
pythonarraysvectorscalar
jazzblue
jazzblue

Reputation: 2437

How to define list/array as a scalar in Python

The title might seem a little weird, but here is what I need to do in Python:

Suppose I have a list (L) and a Boolean array (A)

L=[1,2,3,4] 
A=[True, False, True]

I need to create a list that will have L where A is True and False, where A is false, i.e.

[[1,2,3,4], False, [1,2,3,4]]

I was thinking about doing something like
L and A
but it does not seem to work since L is not a scalar as I want it to be.

Is there any way to define L as a scalar and accomplish it with one-two lines of code?

Thanks.

Upvotes: 2

Views: 1836

Answers (4)

siddharthlatest
siddharthlatest

Reputation: 2257

By definition, L and A are not scalar. You can use a scalar which iterates over A and returns a vector containing L where the scalar is True and containing False where it is False.

Using list comprehension:

[L if a else False for a in A]    # a is the scalar here.

Using map(...):

map(lambda a: L if a else False, A)

Using a for statement:

returnVector = A[:]    # returnVector is the intended output vector
for index, a in enumerate(A): if a is True: returnVector[index] = L

Upvotes: 0

Ryan Morlok
Ryan Morlok

Reputation: 806

map(lambda x: L if x else False, A)

Upvotes: 1

jurgenreza
jurgenreza

Reputation: 6086

You could use list comprehensions:

[L if i else False for i in A ]

Upvotes: 4

Michael Scott Asato Cuthbert
Michael Scott Asato Cuthbert

Reputation: 3638

here's a pretty straightforward way to do it:

newList = []
for x in A:
   if x is True:
       newList.append(L)
   else: 
       newList.append(False)

but since you wanted brevity, here's a one-liner:

[L if x else x for x in A]

Upvotes: 2

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