R: Arrow expressions

Expression {arrow} | R Documentation

## Arrow expressions

### Description

`Expression`s are used to define filter logic for passing to a Dataset Scanner.

`Expression$scalar(x)` constructs an `Expression` which always evaluates to the provided scalar (length-1) R value.

`Expression$field_ref(name)` is used to construct an `Expression` which evaluates to the named column in the `Dataset` against which it is evaluated.

`Expression$compare(OP, e1, e2)` takes two `Expression` operands, constructing an `Expression` which will evaluate these operands then compare them with the relation specified by OP (e.g. "==", "!=", ">", etc.) For example, to filter down to rows where the column named "alpha" is less than 5: `Expression$compare("<", Expression$field_ref("alpha"), Expression$scalar(5))`

`Expression$and(e1, e2)`, `Expression$or(e1, e2)`, and `Expression$not(e1)` construct an `Expression` combining their arguments with Boolean operators.

`Expression$is_valid(x)` is essentially (an inversion of) `is.na()` for `Expression`s.

`Expression$in_(x, set)` evaluates x and returns whether or not it is a member of the set.

[Package arrow version 1.0.1 Index]