I have some code that manipulates a Pandas Dataframe containing Covid-19 vaccine data and displays it on Matplotlib.

The data is here: https://covid.ourworldindata.org/data/owid-covid-data.csv (downloads CSV).

I have manipulated the data so that it only shows countries whose current vaccine per hundred rate is less than 10 (so it can't remove all vaccine rates less than ten, it has to go through each country, get the latest vaccine per hundred rate, and if it is less than ten, remove that country from the graph).

This is highly time-sensitive and needs to be done as quickly as possible.


import pandas as pd
import matplotlib.pyplot as plt
from matplotlib.dates import DateFormatter, WeekdayLocator
import datetime

df = pd.read_csv(
    usecols=["date", "location", "total_vaccinations_per_hundred"], 

df = df[df["total_vaccinations_per_hundred"].notna()]
countries = df["location"].unique().tolist()
countries_copy = countries.copy()

main_country = "United States"

for country in countries:
    if country in countries:
        df_with_current_country = df[df['location']==country]
        if df_with_current_country[df["date"]==df_with_current_country["date"].max()]["total_vaccinations_per_hundred"].tolist()[0] < 10:
            if country != main_country: countries_copy.remove(country)

countries = countries_copy
df = df[df["location"].isin(countries)]

pivot = pd.pivot_table(
    data=df,                                    # What dataframe to use
    index="date",                               # The "rows" of your dataframe
    columns="location",                         # What values to show as columns
    values="total_vaccinations_per_hundred",    # What values to aggregate
    aggfunc="mean",                             # How to aggregate data

pivot = pivot.fillna(method="ffill")

# Step 4: Plot all countries
fig, ax = plt.subplots(figsize=(12,8))
fig.patch.set_facecolor("#F5F5F5")    # Change background color to a light grey
ax.patch.set_facecolor("#F5F5F5")     # Change background color to a light grey

for country in countries:
    if country == main_country:
        country_color = "#129583"
        alpha_color = 1.0
        country_color = "grey"
        alpha_color = 0.75
        pivot.index,              # What to use as your x-values
        pivot[country],           # What to use as your y-values
        color=country_color,    # How to color your line
        alpha=alpha_color     # What transparency to use for your line
    if country_color != "grey":
            x = pivot.index[-1] + datetime.timedelta(days=2),    # Where to position your text relative to the x-axis
            y = pivot[country].max(),                   # How high to position your text
            color = country_color,                    # What color to give your text
            s = country,                                # What to write
            alpha=alpha_color                       # What transparency to use

# Step 5: Configures axes
## A) Format what shows up on axes and how it"s displayed 
date_form = DateFormatter("%Y-%m-%d")
ax.xaxis.set_major_locator(WeekdayLocator(byweekday=(0), interval=1))

## B) Customizing axes and adding a grid

## C) Adding a title and axis labels
plt.ylabel("Total Vaccinations per 100 People", fontsize=12, alpha=0.9)
plt.xlabel("Date", fontsize=12, alpha=0.9)
plt.title("COVID-19 Vaccinations over Time", fontsize=18, weight="bold", alpha=0.9)

# D) Celebrate!

1 Answer 1


The loop and countries section can be replaced with a single DataFrameGroupBy.filter:

  • .groupby('location') - group by country
  • .sort_values('date') - sort country by date (newest at end)
  • .tail(1) >= 10 - only keep countries whose newest rate is at least 10
  • | (country.name == main_country) - always keep main_country
df2 = df.copy() # deep copy original df before loop (only to compare later)

df2 = df2.groupby('location').filter(lambda country:
    (country.sort_values('date').total_vaccinations_per_hundred.tail(1) >= 10)
    | (country.name == main_country)

#       location       date  total_vaccinations_per_hundred
# 1930   Andorra 2021-01-25                            0.75
# 1937   Andorra 2021-02-01                            1.34
# ...        ...        ...                             ...
# 74507  Uruguay 2021-03-26                           14.31
# 74508  Uruguay 2021-03-27                           14.68
# [3507 rows x 3 columns]

And if we run the countries section, we can verify that the filtered df2 matches the looped df:

df2.equals(df) # compare with df after loop

# True
  • 1
    \$\begingroup\$ Nice answer; small comment: the original code kept main_country even if it had less than 10 vaccinations per 100. \$\endgroup\$
    – RootTwo
    Mar 29, 2021 at 4:06
  • \$\begingroup\$ @RootTwo Ah good catch, fixed. \$\endgroup\$
    – tdy
    Mar 29, 2021 at 4:28

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