[python] Normalizing a list of numbers in Python

I need to normalize a list of values to fit in a probability distribution, i.e. between 0.0 and 1.0.

I understand how to normalize, but was curious if Python had a function to automate this.

I'd like to go from:

raw = [0.07, 0.14, 0.07]  

to

normed = [0.25, 0.50, 0.25]

There isn't any function in the standard library (to my knowledge) that will do it, but there are absolutely modules out there which have such functions. However, its easy enough that you can just write your own function:

def normalize(lst):
    s = sum(lst)
    return map(lambda x: float(x)/s, lst)

Sample output:

>>> normed = normalize(raw)
>>> normed
[0.25, 0.5, 0.25]

Try this :

from __future__ import division

raw = [0.07, 0.14, 0.07]  

def norm(input_list):
    norm_list = list()

    if isinstance(input_list, list):
        sum_list = sum(input_list)

        for value in input_list:
            tmp = value  /sum_list
            norm_list.append(tmp) 

    return norm_list

print norm(raw)

This will do what you asked. But I will suggest to try Min-Max normalization.

min-max normalization :

def min_max_norm(dataset):
    if isinstance(dataset, list):
        norm_list = list()
        min_value = min(dataset)
        max_value = max(dataset)

        for value in dataset:
            tmp = (value - min_value) / (max_value - min_value)
            norm_list.append(tmp)

    return norm_list

If you consider using numpy, you can get a faster solution.

import random, time
import numpy as np

a = random.sample(range(1, 20000), 10000)
since = time.time(); b = [i/sum(a) for i in a]; print(time.time()-since)
# 0.7956490516662598

since = time.time(); c=np.array(a);d=c/sum(a); print(time.time()-since)
# 0.001413106918334961

if your list has negative numbers, this is how you would normalize it

a = range(-30,31,5)
norm = [(float(i)-min(a))/(max(a)-min(a)) for i in a]

How long is the list you're going to normalize?

def psum(it):
    "This function makes explicit how many calls to sum() are done."
    print "Another call!"
    return sum(it)

raw = [0.07,0.14,0.07]
print "How many calls to sum()?"
print [ r/psum(raw) for r in raw]

print "\nAnd now?"
s = psum(raw)
print [ r/s for r in raw]

# if one doesn't want auxiliary variables, it can be done inside
# a list comprehension, but in my opinion it's quite Baroque    
print "\nAnd now?"
print [ r/s  for s in [psum(raw)] for r in raw]

Output

# How many calls to sum()?
# Another call!
# Another call!
# Another call!
# [0.25, 0.5, 0.25]
# 
# And now?
# Another call!
# [0.25, 0.5, 0.25]
# 
# And now?
# Another call!
# [0.25, 0.5, 0.25]

Use scikit-learn:

from sklearn.preprocessing import MinMaxScaler
data = np.array([1,2,3]).reshape(-1, 1)
scaler = MinMaxScaler()
scaler.fit(data)
print(scaler.transform(data))

If working with data, many times pandas is the simple key

This particular code will put the raw into one column, then normalize by column per row. (But we can put it into a row and do it by row per column, too! Just have to change the axis values where 0 is for row and 1 is for column.)

import pandas as pd


raw = [0.07, 0.14, 0.07]  

raw_df = pd.DataFrame(raw)
normed_df = raw_df.div(raw_df.sum(axis=0), axis=1)
normed_df

where normed_df will display like:

    0
0   0.25
1   0.50
2   0.25

and then can keep playing with the data, too!

try:

normed = [i/sum(raw) for i in raw]

normed
[0.25, 0.5, 0.25]

For ones who wanna use scikit-learn, you can use

from sklearn.preprocessing import normalize

x = [1,2,3,4]
normalize([x]) # array([[0.18257419, 0.36514837, 0.54772256, 0.73029674]])
normalize([x], norm="l1") # array([[0.1, 0.2, 0.3, 0.4]])
normalize([x], norm="max") # array([[0.25, 0.5 , 0.75, 1.]])