Extract Parts of a Polars Object

Description

Mimics the behavior of [x[i, j, drop = TRUE]][Extract] for data.frame or R vector.

Usage

## S3 method for class 'RPolarsDataFrame'
x[i, j, drop = TRUE]

# S3 method for class 'RPolarsLazyFrame'
x[i, j, drop = TRUE]

# S3 method for class 'RPolarsSeries'
x[i]

Arguments

x	A DataFrame, LazyFrame, or Series
i	Rows to select. Integer vector, logical vector, or an Expression.
j	Columns to select. Integer vector, logical vector, character vector, or an Expression. For LazyFrames, only an Expression can be used.
drop	Convert to a Polars Series if only one column is selected. For LazyFrames, if the result has one column and drop = TRUE, an error will occur.

Details

<Series>[i] is equivalent to pl$select(<Series>)[i, , drop = TRUE].

See Also

<DataFrame>$select(), <LazyFrame>$select(), <DataFrame>$filter(), <LazyFrame>$filter()

Examples

library("polars")

df = as_polars_df(data.frame(a = 1:3, b = letters[1:3]))
lf = df$lazy()

# Select a row
df[1, ]

#> shape: (1, 2)
#> ┌─────┬─────┐
#> │ a   ┆ b   │
#> │ --- ┆ --- │
#> │ i32 ┆ str │
#> ╞═════╪═════╡
#> │ 1   ┆ a   │
#> └─────┴─────┘

# If only `i` is specified, it is treated as `j`
# Select a column
df[1]

#> shape: (3, 1)
#> ┌─────┐
#> │ a   │
#> │ --- │
#> │ i32 │
#> ╞═════╡
#> │ 1   │
#> │ 2   │
#> │ 3   │
#> └─────┘

# Select a column by name (and convert to a Series)
df[, "b"]

#> polars Series: shape: (3,)
#> Series: 'b' [str]
#> [
#>  "a"
#>  "b"
#>  "c"
#> ]

# Can use Expression for filtering and column selection
lf[pl$col("a") >= 2, pl$col("b")$alias("new"), drop = FALSE] |>
  as.data.frame()

#>   new
#> 1   b
#> 2   c