Expressions¶

An expression is a value of type ur.Expr. See Concepts: Expressions for how they are used.

Constructors¶

Function	Expression
`ur.col(name: str)`	The column `name`.
`ur.lit(value)`	A constant: a number, a string, or a boolean.
`ur.src()`	The source column of the ambient `EdgeFrame`.
`ur.dst()`	The destination column of the ambient `EdgeFrame`.
`ur.id()`	The id column of the ambient `NodeFrame`.

ur.src(), ur.dst(), and ur.id() resolve only where a frame with that role is ambient. Elsewhere they raise NotImplementedError.

Operators¶

Kind	Operators	Result
Arithmetic	`+`, `-`, `*`, `/`	numeric
Comparison	`>`, `>=`, `<`, `<=`, `==`, `!=`	boolean
Boolean	`&`, `\|`, `~`	boolean

Each operator accepts an expression or a plain Python value on either side. A plain value becomes a literal.

A filter predicate is any boolean expression. A comparison can compare a column with a literal or with another column.

Aggregations¶

Method	Meaning
`.mean()`	The arithmetic mean.
`.sum()`	The sum.
`.min()`	The minimum.
`.max()`	The maximum.
`.count()`	The number of non-null values.
`.n_unique()`	The number of distinct values.

An aggregation is valid inside group_by().agg() and neighbors().agg().

Naming¶

Method	Meaning
`.alias(name: str)`	Names the output column.

Without an alias, an aggregation in group_by().agg() is named after its column. A keyword argument also names the output: .agg(total=ur.col("x").sum()).

`repr`¶

repr(expr) prints the expression tree. frame.explain() prints the expressions in a plan the same way.