How do i calculate the percentage increase or decrease in a list of values with python

Question

I want to calculate the percentage change either increase or decrease in a list. here is my list ages = [20.3, 30.5, 20.3, 45.5, 50.6, 29.5, 13.4, 140.9]

here is my code

def percent_change_in_naira(value):
  try:
    for i in value:
        if old_num > new_num:
          ((((old_num-new_num)/old_num)*100))
        elif old_num == new_num:
          0
        else:
          ((((new_num-old_num)/old_num)*100))
    return value
  except ZeroDivisionError:
        return 0

How do assign 'new_num' to a new number on the list above and 'old_num' to a previous number on the list above?

Thanks in advance

Answer 1

In Python (as suggested by @sahasrara62 in the comments)

ages = [20.3, 30.5, 20.3, 45.5, 50.6, 29.5, 13.4, 140.9]

changes = []
for x1, x2 in zip(ages[:-1], ages[1:]):
    try:
        pct = (x2 - x1) * 100 / x1
    except ZeroDivisionError:
        pct = None
    changes.append(pct)

# [50.2463054187192,
#  -33.44262295081967,
#  124.13793103448275,
#  11.208791208791212,
#  -41.699604743083,
#  -54.576271186440685,
#  951.4925373134328]

Using numpy

import numpy as np

ages = np.array([20.3, 30.5, 20.3, 45.5, 50.6, 29.5, 
                 13.4, 140.9])
diff = ages[1:] - ages[:-1]
changes = diff * 100 / ages[:-1]

# [ 50.24630542 -33.44262295 124.13793103  11.20879121
#  -41.69960474 -54.57627119 951.49253731]

Using Pandas

import pandas as pd

ages = pd.Series([20.3, 30.5, 20.3, 45.5, 50.6, 29.5, 
                  13.4, 140.9])
changes = ages.pct_change() * 100

# 0           NaN
# 1     50.246305
# 2    -33.442623
# 3    124.137931
# 4     11.208791
# 5    -41.699605
# 6    -54.576271
# 7    951.492537
# dtype: float64