How do you divide each element in a list by an int?
PythonPython Problem Overview
I just want to divide each element in a list by an int.
myList = [10,20,30,40,50,60,70,80,90]
myInt = 10
newList = myList/myInt
This is the error:
TypeError: unsupported operand type(s) for /: 'list' and 'int'
I understand why I am receiving this error. But I am frustrated that I can't find a solution.
Also tried:
newList = [ a/b for a, b in (myList,myInt)]
Error:
ValueError: too many values to unpack
Expected Result:
newList = [1,2,3,4,5,6,7,8,9]
EDIT:
The following code gives me my expected result:
newList = []
for x in myList:
newList.append(x/myInt)
But is there an easier/faster way to do this?
Python Solutions
Solution 1 - Python
The idiomatic way would be to use list comprehension:
myList = [10,20,30,40,50,60,70,80,90]
myInt = 10
newList = [x / myInt for x in myList]
or, if you need to maintain the reference to the original list:
myList[:] = [x / myInt for x in myList]
Solution 2 - Python
The way you tried first is actually directly possible with numpy:
import numpy
myArray = numpy.array([10,20,30,40,50,60,70,80,90])
myInt = 10
newArray = myArray/myInt
If you do such operations with long lists and especially in any sort of scientific computing project, I would really advise using numpy.
Solution 3 - Python
>>> myList = [10,20,30,40,50,60,70,80,90]
>>> myInt = 10
>>> newList = map(lambda x: x/myInt, myList)
>>> newList
[1, 2, 3, 4, 5, 6, 7, 8, 9]
Solution 4 - Python
The abstract version can be:
import numpy as np
myList = [10, 20, 30, 40, 50, 60, 70, 80, 90]
myInt = 10
newList = np.divide(myList, myInt)
Solution 5 - Python
myList = [10,20,30,40,50,60,70,80,90]
myInt = 10
newList = [i/myInt for i in myList]
Solution 6 - Python
myInt=10
myList=[tmpList/myInt for tmpList in range(10,100,10)]
Solution 7 - Python
I was running some of the answers to see what is the fastest way for a large number. So, I found that we can convert the int to an array and it can give the correct results and it is faster.
arrayint=np.array(myInt)
newList = myList / arrayint
This a comparison of all answers above
import numpy as np
import time
import random
myList = random.sample(range(1, 100000), 10000)
myInt = 10
start_time = time.time()
arrayint=np.array(myInt)
newList = myList / arrayint
end_time = time.time()
print(newList,end_time-start_time)
start_time = time.time()
newList = np.array(myList) / myInt
end_time = time.time()
print(newList,end_time-start_time)
start_time = time.time()
newList = [x / myInt for x in myList]
end_time = time.time()
print(newList,end_time-start_time)
start_time = time.time()
myList[:] = [x / myInt for x in myList]
end_time = time.time()
print(newList,end_time-start_time)
start_time = time.time()
newList = map(lambda x: x/myInt, myList)
end_time = time.time()
print(newList,end_time-start_time)
start_time = time.time()
newList = [i/myInt for i in myList]
end_time = time.time()
print(newList,end_time-start_time)
start_time = time.time()
newList = np.divide(myList, myInt)
end_time = time.time()
print(newList,end_time-start_time)
start_time = time.time()
newList = np.divide(myList, myInt)
end_time = time.time()
print(newList,end_time-start_time)
Solution 8 - Python
list = [2,4,8]
new_list = [x//2 for x in list]
print(new_list)
Output:
[1, 2, 4]