R: Arrow expressions

Expression {arrow} | R Documentation

## Arrow expressions

### Description

`Expression`s are used to define filter logic for passing to a Dataset Scanner. `FieldExpression`s refer to columns in the `Dataset` and are compared to `ScalarExpression`s using `ComparisonExpression`s. `ComparisonExpression`s may be combined with `AndExpression` or `OrExpression` and negated with `NotExpression`. `IsValidExpression` is essentially `is.na()` for `Expression`s.

### Factory

`FieldExpression$create(name)` takes a string name as input. This string should refer to a column in a `Dataset` at the time it is evaluated, but you can construct a `FieldExpression` independently of any `Dataset`.

`ScalarExpression$create(x)` takes a scalar (length-1) R value as input.

`ComparisonExpression$create(OP, e1, e2)` takes a string operator name (e.g. "==", "!=", ">", etc.) and two `Expression` objects.

`AndExpression$create(e1, e2)` and `OrExpression$create(e1, e2)` take two `Expression` objects, while `NotExpression$create(e1)` and `IsValidExpression$create(e1)` take a single `Expression`.

[Package arrow version 0.17.1 Index]