Finding missing element in a list in Python
Question:
I have two lists J2 and J10. I am trying to find the elements in J10 which are absent in J2 but I am getting an error. I present the expected output.
J2=[128, 4, 6, 7, 8, 9, 10]
J10=[4, 6, 7, 8, 9, 10, 13, 128]
J=[i for i in J10 not in J2]
print(J)
The error is
in <module>
J=[i for i in J10 not in J2]
TypeError: 'bool' object is not iterable
The expected output is
[13]
Answers:
J=[i for i in J10 if i not in J2]
Or:
lst=[]
for i in J10:
if i not in J2:
lst.append(i)
#[13]
Or
set(J10)-(set(J2))
This will do the job:
temp = list(filter(lambda x: x not in J2, J10))
print(temp)
Here is why your code fails:
J10 not in J2 is treated as an expression that checks if J10 (as a whole is in J2). In other words, the J10 not in J2 will be either True or False and since a boolean is not a storage-like element such as a list, you can not iterate it.
if you want to solve your problem with syntax you were trying, you should use:
J=[i for i in J10 if i not in J2]
print(set(J2).symmetric_difference(J10))
Your code does not work because it’s parsed as:
[i for i in (J10 not in J2)]
J10 not in J2 returns a boolean value that you can’t iterate over. You are missing an if.
[i for i in J10 if i not in J2]
Sets may be useful here, though, as the membership check if O(len(J2)) and the outer loop is O(len(J10)), making this a potentially quite expensive approach.
>>> set(J10) ^ set(J2) & set(J10)
{13}
First we find the set of items that are unique to each set. TO ensure this contains only unique elements from J10, we then intersect with J10.
Try this way..
J2=[128, 4, 6, 7, 8, 9, 10]
J10=[4, 6, 7, 8, 9, 10, 13, 128]
J=list(set(J10).difference(J2))
print(J)
J=[i for i in J10 if i not in J2]
I have two lists J2 and J10. I am trying to find the elements in J10 which are absent in J2 but I am getting an error. I present the expected output.
J2=[128, 4, 6, 7, 8, 9, 10]
J10=[4, 6, 7, 8, 9, 10, 13, 128]
J=[i for i in J10 not in J2]
print(J)
The error is
in <module>
J=[i for i in J10 not in J2]
TypeError: 'bool' object is not iterable
The expected output is
[13]
J=[i for i in J10 if i not in J2]
Or:
lst=[]
for i in J10:
if i not in J2:
lst.append(i)
#[13]
Or
set(J10)-(set(J2))
This will do the job:
temp = list(filter(lambda x: x not in J2, J10))
print(temp)
Here is why your code fails:
J10 not in J2 is treated as an expression that checks if J10 (as a whole is in J2). In other words, the J10 not in J2 will be either True or False and since a boolean is not a storage-like element such as a list, you can not iterate it.
if you want to solve your problem with syntax you were trying, you should use:
J=[i for i in J10 if i not in J2]
print(set(J2).symmetric_difference(J10))
Your code does not work because it’s parsed as:
[i for i in (J10 not in J2)]
J10 not in J2 returns a boolean value that you can’t iterate over. You are missing an if.
[i for i in J10 if i not in J2]
Sets may be useful here, though, as the membership check if O(len(J2)) and the outer loop is O(len(J10)), making this a potentially quite expensive approach.
>>> set(J10) ^ set(J2) & set(J10)
{13}
First we find the set of items that are unique to each set. TO ensure this contains only unique elements from J10, we then intersect with J10.
Try this way..
J2=[128, 4, 6, 7, 8, 9, 10]
J10=[4, 6, 7, 8, 9, 10, 13, 128]
J=list(set(J10).difference(J2))
print(J)
J=[i for i in J10 if i not in J2]