Create a List for Boolean Mask.

[leoahum]

Hi all,

I am trying to find a better way to create a Boolean Mask based on certain conditions. Here is the question and my way to answer it.

Question:
l = ["a","b","a","c"], "a" is a qualified data for the future use. Create a list with boolean values.

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l = ["a","b","a","c"] L = [] for i in l:     if i == "a":         L.append(True)     else:         L.append(False)

Result:
L = [True,False,True,False]

Thanks!

[ichabod801]

You don't need the conditional. Just append i == 'a'.

[leoahum]

You don't need the conditional. Just append i == 'a'.

Hi ichabod801, thanks for the solution.

Base on your reply, I tried a further simplification,

1 2	l = ["a","b","a","c"] L = [x for x == 'a' in l]

python told me "invalid syntax"

Could you tell me the reason for this failure?

[micseydel]

You want

1	[x == 'a' for x in l]

[leoahum]

You want

1	[x == 'a' for x in l]

Wow,it's like magic. Thanks!