Pythonpolars：要列表的字符串列到整型列

目前的方法可以修改:

• .strip_chars()表示删除尾随逗号
• .cast(pl.List(pl.Int32))一次投下所有的东西
• 传递一个函数到.to_struct(fields=)以"动态地"重命名字段

cols = "blockSizes", "blockStarts"

(df.with_columns(
    pl.col(col)
      .str.strip_chars(",")
      .str.split(",")
      .cast(pl.List(pl.Int32))
      .list.to_struct(
         n_field_strategy = "max_width", 
         fields = lambda idx, col=col: f"{col}_{idx}"
      )
    for col in cols
 )
 .unnest(cols)
)

shape: (4, 5)
┌───────┬──────────────┬──────────────┬───────────────┬───────────────┐
│ chrom ┆ blockSizes_0 ┆ blockSizes_1 ┆ blockStarts_0 ┆ blockStarts_1 │
│ ---   ┆ ---          ┆ ---          ┆ ---           ┆ ---           │
│ str   ┆ i32          ┆ i32          ┆ i32           ┆ i32           │
╞═══════╪══════════════╪══════════════╪═══════════════╪═══════════════╡
│ 1     ┆ 10           ┆ 29           ┆ 0             ┆ 50            │
│ 1     ┆ 20           ┆ 22           ┆ 0             ┆ 45            │
│ 2     ┆ 30           ┆ 25           ┆ 0             ┆ 60            │
│ X     ┆ 40           ┆ 23           ┆ 0             ┆ 70            │
└───────┴──────────────┴──────────────┴───────────────┴───────────────┘

也许创建一个函数会让事情变得更整洁.

def csv_to_struct(col):
    expr = pl.col(col).str.strip_chars(",").str.split(",")
    expr = expr.cast(pl.List(pl.Int32))
    return expr.list.to_struct(
        n_field_strategy = "max_width", 
        fields = lambda idx: f"{col}_{idx}"
    )

cols = "blockSizes", "blockStarts"

df.with_columns(map(csv_to_struct, cols)).unnest(cols)

熔化/枢轴

另一种方法是使用.melt()+.pivot()

cols = "blockSizes", "blockStarts"

(df.with_row_count()
   .with_columns(
      pl.col(cols).str.strip_chars(",").str.split(",").cast(pl.List(int))
   )
   .explode(cols)
   .melt(["row_nr", "chrom"], variable_name="name")
   .with_columns(
      pl.format("{}_{}", "name", pl.col("row_nr").cum_count().over("row_nr", "name"))
   )
   .pivot("value", ["row_nr", "chrom"], "name")
)

shape: (4, 6)
┌────────┬───────┬──────────────┬──────────────┬───────────────┬───────────────┐
│ row_nr ┆ chrom ┆ blockSizes_0 ┆ blockSizes_1 ┆ blockStarts_0 ┆ blockStarts_1 │
│ ---    ┆ ---   ┆ ---          ┆ ---          ┆ ---           ┆ ---           │
│ u32    ┆ str   ┆ i64          ┆ i64          ┆ i64           ┆ i64           │
╞════════╪═══════╪══════════════╪══════════════╪═══════════════╪═══════════════╡
│ 0      ┆ 1     ┆ 10           ┆ 29           ┆ 0             ┆ 50            │
│ 1      ┆ 1     ┆ 20           ┆ 22           ┆ 0             ┆ 45            │
│ 2      ┆ 2     ┆ 30           ┆ 25           ┆ 0             ┆ 60            │
│ 3      ┆ X     ┆ 40           ┆ 23           ┆ 0             ┆ 70            │
└────────┴───────┴──────────────┴──────────────┴───────────────┴───────────────┘