Python program to count positive and negative numbers in a list
Last Updated :
10 Apr, 2023
Given a list of numbers, write a Python program to count positive and negative numbers in a List.
Example:
Input: list1 = [2, -7, 5, -64, -14]
Output: pos = 2, neg = 3
Input: list2 = [-12, 14, 95, 3]
Output: pos = 3, neg = 1
Example #1: Count positive and negative numbers from the given list using for loop Iterate each element in the list using for loop and check if num >= 0, the condition to check positive numbers. If the condition satisfies, then increase pos_count else increase neg_count.
Python3
list1 = [10, -21, 4, -45, 66, -93, 1]
pos_count, neg_count = 0, 0
for num in list1:
if num >= 0:
pos_count += 1
else:
neg_count += 1
print("Positive numbers in the list: ", pos_count)
print("Negative numbers in the list: ", neg_count)
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Output
Positive numbers in the list: 4
Negative numbers in the list: 3
Time Complexity: O(N), Here N is the number of items in the list.
Auxiliary Space: O(1), As constant extra space is used.
Example #2: Using while loop
Python3
list1 = [-10, -21, -4, -45, -66, 93, 11]
pos_count, neg_count = 0, 0
num = 0
while(num < len(list1)):
if list1[num] >= 0:
pos_count += 1
else:
neg_count += 1
num += 1
print("Positive numbers in the list: ", pos_count)
print("Negative numbers in the list: ", neg_count)
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Output
Positive numbers in the list: 2
Negative numbers in the list: 5
Time Complexity: O(N), Here N is the number of items in the list.
Auxiliary Space: O(1), As constant extra space is used.
Example #3: Using Python Lambda Expressions
Python3
list1 = [10, -21, -4, 45, 66, 93, -11]
neg_count = len(list(filter(lambda x: (x < 0), list1)))
pos_count = len(list(filter(lambda x: (x >= 0), list1)))
print("Positive numbers in the list: ", pos_count)
print("Negative numbers in the list: ", neg_count)
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Output
Positive numbers in the list: 4
Negative numbers in the list: 3
Time Complexity: O(N), Here N is the number of items in the list.
Auxiliary Space: O(1), As constant extra space is used.
Example #4: Using List Comprehension
Python3
list1 = [-10, -21, -4, -45, -66, -93, 11]
only_pos = [num for num in list1 if num >= 1]
pos_count = len(only_pos)
print("Positive numbers in the list: ", pos_count)
print("Negative numbers in the list: ", len(list1) - pos_count)
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Output
Positive numbers in the list: 1
Negative numbers in the list: 6
Time Complexity: O(N), Here N is the number of items in the list.
Auxiliary Space: O(1), As constant extra space is used.
Method: Using enumerate function
Python3
l=[12, -7, 5, 64, -14];c=0
x=[a for j,a in enumerate(l) if a>=0]
print("Length of Positive numbers is:", len(x))
print("Length of Negative numbers is:", len(l)-len(x))
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Output
Length of Positive numbers is: 3
Length of Negative numbers is: 2
Time Complexity: O(N), Here N is the number of items in the list.
Auxiliary Space: O(1), As constant extra space is used.
Method : Using startswith() method
Python3
list1 = [10, -21, 4, -45, 66, -93, 1,0]
pos_count, neg_count = 0, 0
list2=list(map(str,list1))
for num in list2:
if num.startswith("-"):
neg_count += 1
elif(num!="0"):
if(not num.startswith("-")):
pos_count+=1
print("Positive numbers in the list: ", pos_count)
print("Negative numbers in the list: ", neg_count)
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Output
Positive numbers in the list: 4
Negative numbers in the list: 3
Time Complexity: O(N), Here N is the number of items in the list.
Auxiliary Space: O(1), As constant extra space is used.
Method: Using sum() method
Python3
l = [12, -7, 5, 64, -14];
x = sum(1 for i in l if i >= 0 )
print("Length of Positive numbers is:", x)
print("Length of Negative numbers is:", len(l)-x)
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Output
Length of Positive numbers is: 3
Length of Negative numbers is: 2
Time Complexity: O(N), Here N is the number of items in the list.
Auxiliary Space: O(1), As constant extra space is used.
Method : Using for loop
STEP BY STEP APPROACH :
- Initialize a list of numbers called list1 with integer values.
- Initialize two variables pos_count and neg_count to 0.
- Convert all the numbers in list1 to strings using the map() function and store them in a new list called list2.
- Iterate through each number num in list2 using a for loop.
- For each number num, check the first character of the string representation of the number using num[0]:
a. If the first character is “-“, increment the neg_count variable as the number is negative.
b. Else, check if the number is not equal to “0” using num!=”0″:
i. If the number is positive, increment the pos_count variable.
- Print the final values of pos_count and neg_count using the print() function.
Python3
list1 = [10, -21, 4, -45, 66, -93, 1,0]
pos_count, neg_count = 0, 0
list2=list(map(str,list1))
for num in list2:
if num[0]=="-":
neg_count += 1
elif(num!="0"):
if(not num[0]=="-"):
pos_count+=1
print("Positive numbers in the list: ", pos_count)
print("Negative numbers in the list: ", neg_count)
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Output
Positive numbers in the list: 4
Negative numbers in the list: 3
Time Complexity: O(N)
Auxiliary Space: O(N)
Method: Using the collections module and the Counter() function:
- Importing the Counter class from the collections module.
- Using a list comprehension to get a list of boolean values to check whether each number is non-negative or not, based on whether it is greater than or equal to zero.
- Passing the list of booleans to the Counter to get a dictionary mapping for counts.
- Storing the count of positive and negative no.
- Printing the output.
Python3
from collections import Counter
list1 = [10, -21, 4, -45, 66, -93, 1,0]
counts = Counter(num > 0 for num in list1)
pos_count = counts[True]
neg_count = counts[False] - (0 in list1)
print("Positive numbers in the list: ", pos_count)
print("Negative numbers in the list: ", neg_count)
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Output
Positive numbers in the list: 4
Negative numbers in the list: 3
Time Complexity: O(N) as we are traversing the whole list which takes O(N) time complexity.
Auxiliary Space: O(1) as no extra memory is used.
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