Preview data
Quickly inspect the beginning of a newly loaded or transformed table.
Polars · Module
df.head
Returns the first n rows of a Polars DataFrame. By default, it returns five rows; a negative n omits that many rows from the end.
How it works
Call head on a DataFrame to obtain a new DataFrame containing the first requested rows. The default is five rows; passing a negative number instead excludes that many rows from the end, which is useful when inspecting nearly all data while omitting a tail.
Syntax
DataFrame.head(*n: int = 5*) → DataFrameParameters
| Name | Type | Description |
|---|---|---|
n | int = 5 | Number of rows to return. A negative value returns all rows except the last abs(n). |
Returns
A DataFrame containing the selected leading rows.
Key points
- Returns the leading n rows of the DataFrame.
- The signature accepts an integer n and defaults it to 5.
- The n argument controls how many rows the result should contain.
- Negative values exclude the corresponding number of rows from the DataFrame's end.
Common mistakes
- A negative n does not mean “take rows from the end”; it returns every row except the last abs(n).
Example: Inspect the first rows
import polars as pl
df = pl.DataFrame({"id": [1, 2, 3], "name": ["Ada", "Linus", "Grace"]})
print(df.head(2))Creates a DataFrame and returns its first two rows.
When to use it
Validate transformations
Check whether an operation produced the expected leading records.
Exclude trailing rows
Display nearly all rows while excluding a known trailing portion.
Interview questions
QWhat does DataFrame.head return, and what is its default?
DataFrame.head returns the first n rows as a DataFrame, with n defaulting to 5. It is useful for quickly inspecting the beginning of a table.
Follow-up: What does head(-3) do? It returns all rows except the final three.
QWhat is the purpose of the n parameter?
The method accepts one parameter, n, which specifies the number of rows to return. The result preserves the DataFrame form rather than returning a Series or scalar.
Follow-up: How would you inspect only one column? Select that column first, then call head on the resulting DataFrame.
QHow does negative n change the behavior?
A negative n is supported and changes the operation to exclude rows from the end. For example, head(-3) returns all rows other than the last three.
Follow-up: What happens if the exclusion count is larger than the DataFrame? Verify the behavior with a small test DataFrame rather than assuming a fixed output shape.
Related
polars.DataFrame.limitpolars.headpolars.Expr.headpolars.dataframe.group_by.GroupBy.head