计算两个数字之间的百分比变化（Python）

Question

I have a list of prices where I am trying to calculate the change in percentage of each number. I calculated the differences with

    prices = [30.4, 32.5, 31.7, 31.2, 32.7, 34.1, 35.8, 37.8, 36.3, 36.3, 35.6]

    def f():
        for i in range(len(prices)):
            print(prices[i]-prices[i-1])

Which returns the differences like

    2.1
    -0.8
    -0.5
    ...

I know the change in percentage would be ((i-(i-1))/(i-1) *100, but I don't know how to incorporate that into the script. Any help would be much appreciated.

Answer 1

If you haven't been exposed to the pandas library in Python (http://pandas.pydata.org/), you should definitely check it out.

Doing this is as easy as:

import pandas as pd
prices = [30.4, 32.5, 31.7, 31.2, 32.7, 34.1, 35.8, 37.8, 36.3, 36.3, 35.6]

price_series = pd.Series(prices)
price_series.pct_change()

Answer 2

Try this:

prices = [30.4, 32.5, 31.7, 31.2, 32.7, 34.1, 35.8, 37.8, 36.3, 36.3, 35.6]

for a, b in zip(prices[::1], prices[1::1]):
    print 100 * (b - a) / a

Edit: If you want this as a list, you could do this:

print [100 * (b - a) / a for a, b in zip(prices[::1], prices[1::1])]

Answer 3

Though definitely not the most elegant way, if you'd like to define a function it would look something like this:

def pctc(Q):
    output = [0]
    for i in range(len(Q)):
        if i > 0:
            increase = Q[i]-Q[i-1]
            percentage = (increase/Q[i]) * 100
            output.append(percentage)
    return(output)

There's probably even a better way to do that function, but it's clear at least. :))