子集化 DataFrame
Polars 入门
Liam Brannigan
Data Scientist and Polars Contributor
选择行
rentals[0]
shape: (1, 8)
| name | type | price | bedrooms | doubles | singles | review | beach |
| --- | --- | --- | --- | --- | --- | --- | --- |
| str | str | i64 | i64 | i64 | i64 | f64 | bool |
|-----------|---------|-------|----------|---------|---------|--------|-------|
| Seashells | Cottage | 540 | 4 | 2 | 2 | 8.7 | true |
选择行
rentals[-1]
shape: (1, 8)
| name | type | price | bedrooms | doubles | singles | review | beach |
| --- | --- | --- | --- | --- | --- | --- | --- |
| str | str | i64 | i64 | i64 | i64 | f64 | bool |
|---------------------|---------|-------|----------|---------|---------|--------|-------|
| Tehidy Holiday Park | Cottage | 637 | 4 | 2 | 4 | 9.0 | false |
选择一段行
rentals[1:3]
shape: (2, 8)
| name | type | price | bedrooms | doubles | singles | review | beach |
| --- | --- | --- | --- | --- | --- | --- | --- |
| str | str | i64 | i64 | i64 | i64 | f64 | bool |
|-----------|---------|-------|----------|---------|---------|--------|-------|
| Seashells | Cottage | 540 | 4 | 2 | 2 | 8.7 | true |
| Lake view | Cottage | 714 | 3 | 1 | 4 | 9.2 | true |
由 DataFrame 列创建 Series
rentals["name"]
shape: (2,)
Series: 'name' [str]
[
"Waves"
"Seashells"
]
- 在
[]中选单列会得到Series Series适合做可视化
用方括号选择多列
rentals[["name", "price"]]
shape: (5, 2)
| name | price |
| --- | --- |
| str | i64 |
|-------------|-------|
| Waves | 540 |
| Seashells | 540 |
| Lake view | 714 |
| Piran View | 775 |
| Palma Villa | 1772 |
选择行与列
rentals[:3, ["name", "price"]]
shape: (3, 2)
| name | price |
| --- | --- |
| str | i64 |
|-----------|-------|
| Waves | 540 |
| Seashells | 540 |
| Lake view | 714 |
用 .select() 子集化列
rentals.select("name", "price")
shape: (3, 2)
| name | price |
| --- | --- |
| str | i64 |
|-------------|-------|
| Waves | 540 |
| Seashells | 540 |
| Lake view | 714 |
df.select(["name", "price"])
方括号还是 select？
rentals.select("name","price")
shape: (3, 2)
| name | price |
| --- | --- |
| str | i64 |
|-------------|-------|
| Waves | 540 |
| Seashells | 540 |
| Lake view | 714 |
.select() 允许进行优化
rentals[["name","price"]]
shape: (3, 2)
| name | price |
| --- | --- |
| str | i64 |
|-------------|-------|
| Waves | 540 |
| Seashells | 540 |
| Lake view | 714 |
Passons à la pratique !
Polars 入门
