pandas getting max and min for a specific other column value

Question

I have following sample data-set.

 raw_data = {'name': ['Willard Morris', 'Al Jennings', 'Omar Mullins', 'Spencer 
 McDaniel'],
            'age': [20, 19, 22, 21],
            'favorite_color': ['blue', 'blue', 'yellow', "green"],
            'grade': [88, 92, 95, 70]}

 df = pd.DataFrame(raw_data)
 df.head()

I am interested in finding max, min grade for a specific color say 'blue' how can i find it out.

The solution i have is following.. is there a better way. I have a huge data-set performance is also a criteria while selecting options available.

for i in df.index:
    if df.at[i, 'server_ip'] == 'blue':
        if min_grade > df.at[i,'grade']:
           min_grade = df.at[i,'grade']
        if max_grade < df.at[i,'grade']:
           max_grade = df.at[i,'grade']

question has nothing to do with machine-learning - kindly do not spam the tag (removed) — desertnaut
– desertnaut, Commented Jul 5, 2018 at 14:42
df[df.favorite_color == "blue"]["grade"].min() df[df.favorite_color == "blue"]["grade"].max() — Tom Ron
– Tom Ron, Commented Jul 5, 2018 at 14:45
Possible duplicate of Groupby max value and return corresponding row in pandas dataframe — Rushabh Mehta
– Rushabh Mehta, Commented Jul 5, 2018 at 14:52

Rushabh Mehta · Accepted Answer · 2018-07-06 20:22:31Z

1

I would personally use .loc here

df.loc[df['favorite_color']=='blue','grade'].max()
df.loc[df['favorite_color']=='blue','grade'].min()

Edit 1

If you don't want to search twice, just save the result of .loc first then conduct the aggregation

data = df.loc[df['favorite_color']=='blue','grade']
min = data.min()
max = data.max()

Edit 2

If you want to search max and min for every color, use groupby

grouped = df.groupby('favorite_color')['grade']
max = grouped.max()
min = grouped.min()

edited Jul 6, 2018 at 20:22

answered Jul 5, 2018 at 14:50

Rushabh Mehta

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4 Comments

27harishvk Over a year ago

When we are finding max why can't we find min also?. Can't we stop multiple iterations?.

Rushabh Mehta Over a year ago

See edits ... also feel free to hit that green check to the left!

27harishvk Over a year ago

I was looking for a solution to find max and min for all unique values of favorite_color. Any solutions?

Rushabh Mehta Over a year ago

In that case, you should use groupby

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