Viewing first rows
- Machine Learning course
- Beginner
- Lesson 17/112
- 5 min
The head() method returns the first n rows of a DataFrame; default n=5.
head, tail, info
When you open a new dataset, the first thing is to look at it:
df.head() # first 5 rows
df.head(2) # first 2 rows
df.tail(3) # last 3 rows
df.info() # column types and non-null countsinfo() immediately shows missing values and columns read with the wrong type (for example text instead of numbers).
describe and value_counts
A summary of numeric columns is taken with describe(), the distribution of categorical columns with value_counts():
df.describe() # count, mean, std, min, quartiles, max
df["sehir"].value_counts() # how often each value appears
df["yas"].nunique() # number of distinct valuesIn classification problems, applying value_counts() to the label column shows whether the classes are balanced.
Practice Get to know the data
Find how often each city appears in the sehir column with value_counts() and print the count of the most frequent city. Then print the length of the first 2 rows with len(df.head(2)).
Starter code
import pandas as pd
df = pd.DataFrame({"sehir": ["Ankara", "İzmir", "Ankara", "Bursa", "Ankara"]})
# buraya yazSample solution
import pandas as pd
df = pd.DataFrame({"sehir": ["Ankara", "İzmir", "Ankara", "Bursa", "Ankara"]})
sayim = df["sehir"].value_counts()
print(sayim.max())
print(len(df.head(2)))Expected output
3 2
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 How many rows does <code>df.head()</code> show without an argument?
- All
- 5 Correct answer
- 10
- 1
Explanation: The default value of n is 5.
2 Show the last 3 rows.
print(df.____(3))print(df.tail(3))Explanation: tail(n) returns the last n rows.
3 Match the methods.
| Term | Meaning |
|---|---|
head() |
First rows |
info() |
Column types |
describe() |
Numeric summary |
value_counts() |
Value frequencies |