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I am unable to get the correct value for the conditional if statement nested with for loop.Here is an example written in code,

# Input data
d11 = np.matrix([[3,6,1],[6,8,1],[1,1,1],[5,8,9]])
qp1 = np.matrix([[1],[3],[5]])
h1 = np.matrix([[5],[40],[100],[5]])

I need that row of d11 matrix whose value on multiplying with qp1 is less than the corresponding value in h1 i.e d11[i] * qp < h[i].The code for this is,

for x in range(len(d11)):
    if d11[x] * qp1 < h1[x]:
        a = d11[x]
    else:
        a = []

when we multipy d11 and qp1 we get the values as [26,35 , 9 ,22].Thus if we compare with h1, we find the condition is True for 2nd row i.e 35< 40 and 3rd row i.e9 < 100 .So the answer is [[6,8,1],[1,1,1]].But i am unable to get the answer.Please suggest me the correct way..

Manasaveena
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3 Answers3

1

Your if statement is checking whether or not the list created by the list comprehension
[aa[i] > 10 for i in range(len(a))] (ie the list [False, False, False, False]) is empty.

Since it is not empty the if statement is evaluated to True.

Instead, consider using any:

aa = [1, 4, 5, 6]
if any(num > 10 for num in aa):
    c = aa[i],'t'  # as (correctly) pointed out in the comments below,
                   # i is not defined here since we are no longer using an index
                   # to iterate over the list's elements.
                   # You'll need to decide what you want to do in case an element
                   # IS larger than 10.
else:
    c = 0

Your code has another bug: by the time the list comprehension is done, i will always be the last index.

DeepSpace
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1

The list Comprehensions is evalutaed differntly than you think. You are checking whether the list is not empty and return the last element of the list.

What you want is someting like:

aa = [1,4,5,6,101]
c = [elem for elem in aa if elem >10]

If c is not empty, you know that elements above 10 have been in the list.

devnull
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0

Your condition is equivalent to:

if len([aa[i] > 10 for i in range(len(a))]):

ie. you're checking if the list is nonempty. And it is nonempty - it consists of four Falses.

Błotosmętek
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