[FIXED] Changed frequency of ticks in Pandas '.bar' plot, but messed up the actual bars

Issue

how's your self-isolation going on?

Mine rocks, as I'm drilling through visualization in Python. Recently, however, I've ran into an issue.

I figured that .plot.bar() in Pandas has an uncommon formatting of x-axis (which kinda confirms that I read before I ask). I had price data with monthly frequency, so I applied a fix to display only yearly ticks in a bar chart:

fig, ax = plt.subplots()
ax.bar(btc_returns.index, btc_returns)

ax.xaxis.set_major_locator(mdates.YearLocator())
ax.xaxis.set_major_formatter(mdates.DateFormatter('%Y'))

Where btc_returns is a Series object with datetime in index.

The output I got was weird. Here are the screenshots of what I expected vs the end result.

I tried to find a solution to this, but no luck. Can you guys please give me a hand? Thanks! Criticism is welcome as always :)

Solution

• Using the stock value data from Yahoo Finance: Bitcoin USD
• Technically, you can do pd.to_datetime(btc.Date).dt.date at the beginning, but resample won't work, which is why btc_monthly.index.date is done as a second step.
• resample can happen over different periods (e.g. 2M = every two months)

Load and transform the data

import pandas as pd
import matplotlib.pyplot as plt

# load data
btc = pd.read_csv('data/BTC-USD.csv')

# Date to datetime
btc.Date = pd.to_datetime(btc.Date)

# calculate daily return %
btc['return'] = ((btc.Close - btc.Close.shift(1))/btc.Close.shift(1))*100

# resample to monthly and aggregate by sum
btc_monthly = btc.resample('M', on='Date').sum()

# set the index to be date only (no time)
btc_monthly.index = btc_monthly.index.date

Plot

btc_monthly.plot(y='return', kind='bar', figsize=(15, 8))
plt.show()

Plot Bimonthly

btc_monthly = btc.resample('2M', on='Date').sum()  # instead of 'M'
btc_monthly.index = btc_monthly.index.date

btc_monthly.plot(y='return', kind='bar', figsize=(15, 8), legend=False)
plt.title('Bitcoin USD: Bimonthly % Return')
plt.ylabel('% return')
plt.xlabel('Date')
plt.show()

Answered By - Trenton McKinney