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I want to plot changes in monthly values from dataset spanning over few years with matplot.pylib, pandas

I am trying to plot a graph that shows changes in monthly values with matplotlib (python) and pandas, and I am having struggles with it as I am new. Apologies in advance for the formatting.

Here is a sample of dataframe:

  Year    Month      Value
  2014    January     510
  2014    February    542
  2014    March       684
  2014    April       700
  2014    May         732
  2014    July        603
  2014    August      643
  2014    September   680
  2014    October     723
  2014    November    760
  2014    December    810
  2015    January     920
  2015    February    900
  2015    March       780
  2015    April       710
  2015    May         810
  2015    July        895
  2015    August      906
  2015    September   945
  2015    October     980
  2015    November    1000
  2015    December    1123

Here's what i tried (shortened version):

import matplotlib.pyplot as plt    

plt.title('Monthly data over several years')
plt.plot(df['Month'].to_list(), df['Value'].to_list())

This would result in the plotted values for each month in 2015 on the Y axis going back to the previous year's respective month instead of going on the Y axis of 2015's Jan-Dec. For example, 2015 January's value of 920 would go right back to 2014 January on the Y axis.

I also tried:

  months = {"January": 1, "February": 2, "March": 3, "April": 4, "May": 5, "June": 6,
 "July": 7,    "August": 8, "September": 9, "October": 10, "November": 11, "December": 12}
  df{'Month'] = df.Month.map(months)
  df['Date'] = df['Year'].map(str) + '-' + df['Month'].map(str)

This was to concatenate the month with the respective year to avoid the previous problem, however, I just ended up with NaN values in the df['Months'] column. Furthermore, I feel like it would overpopulate the xticks (or labels??) on the x axis, if it did work.

What I want is a time-series like plot graph showing the monthly changes in the values for the two years. I'm struggling to construct the xticks neatly on the graph. Otherwise, would a bar graph work better?

Solution

  • It is much easier if you split Year/month columns to separate series for each year

    import pandas as pd 
import matplotlib.pyplot as plt

fig, axes = plt.subplots(figsize=(6,4))

df = pd.read_csv("data.csv")
df2 = pd.pivot_table(df, index="Month", columns=["Year"])
df2 = df2.reindex(['January', 'February', 'March', 'April', 'May', 'July', 'August', 'September', 'October', 'November', 'December'])
df2.plot(ax=axes)
fig.savefig("plot.png")

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