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Expressions

ColumnRef ​

The ColumnRef class provides a fluent API for building column expressions.

Overview ​

ColumnRef is returned by the col() function and provides chainable methods for creating expressions.

typescript
import { col } from "molniya";

// Create a column reference
const priceCol = col("price");

// Chain methods to build expressions
priceCol.mul(1.1).add(col("tax"));

Creating Column References ​

col() ​

typescript
col(name: string): ColumnRef

Example:

typescript
import { col } from "molniya";

col("id")
col("customer_name")
col("total_amount")

Comparison Methods ​

eq() ​

Equal comparison.

typescript
eq(other: Expr | number | string | boolean): ComparisonExpr

Example:

typescript
col("status").eq("active")
col("id").eq(123)
col("verified").eq(true)

neq() ​

Not equal comparison.

typescript
neq(other: Expr | number | string | boolean): ComparisonExpr

Example:

typescript
col("status").neq("deleted")
col("id").neq(0)

gt() ​

Greater than.

typescript
gt(other: Expr | number): ComparisonExpr

Example:

typescript
col("age").gt(18)
col("price").gt(100)

gte() ​

Greater than or equal.

typescript
gte(other: Expr | number): ComparisonExpr

Example:

typescript
col("score").gte(60)  // Passing grade
col("balance").gte(0)  // Non-negative

lt() ​

Less than.

typescript
lt(other: Expr | number): ComparisonExpr

Example:

typescript
col("age").lt(65)
col("temperature").lt(100)

lte() ​

Less than or equal.

typescript
lte(other: Expr | number): ComparisonExpr

Example:

typescript
col("price").lte(50)  // Budget items

between() ​

Check if value is within a range (inclusive).

typescript
between(low: Expr | number, high: Expr | number): BetweenExpr

Example:

typescript
col("age").between(18, 65)
col("score").between(0, 100)

Null Check Methods ​

isNull() ​

Check if value is null.

typescript
isNull(): NullCheckExpr

Example:

typescript
col("email").isNull()

isNotNull() ​

Check if value is not null.

typescript
isNotNull(): NullCheckExpr

Example:

typescript
col("email").isNotNull()

Arithmetic Methods ​

add() ​

Add to another expression.

typescript
add(other: Expr | number): ArithmeticExpr

Example:

typescript
col("price").add(col("tax"))
col("score").add(10)  // Bonus points

sub() ​

Subtract another expression.

typescript
sub(other: Expr | number): ArithmeticExpr

Example:

typescript
col("total").sub(col("discount"))

mul() ​

Multiply by another expression.

typescript
mul(other: Expr | number): ArithmeticExpr

Example:

typescript
col("price").mul(0.9)  // 10% discount
col("price").mul(col("quantity"))

div() ​

Divide by another expression.

typescript
div(other: Expr | number): ArithmeticExpr

Example:

typescript
col("total").div(col("count"))  // Average

mod() ​

Modulo (remainder) operation.

typescript
mod(other: Expr | number): ArithmeticExpr

Example:

typescript
col("n").mod(2)  // Check even/odd

neg() ​

Negate the value.

typescript
neg(): NegExpr

Example:

typescript
col("debt").neg()  // Negative debt = credit

String Methods ​

contains() ​

Check if string contains a pattern.

typescript
contains(pattern: string): StringOpExpr

Example:

typescript
col("email").contains("@gmail.com")
col("description").contains("urgent")

startsWith() ​

Check if string starts with a pattern.

typescript
startsWith(pattern: string): StringOpExpr

Example:

typescript
col("name").startsWith("Dr.")
col("phone").startsWith("+1")

endsWith() ​

Check if string ends with a pattern.

typescript
endsWith(pattern: string): StringOpExpr

Example:

typescript
col("email").endsWith("@company.com")
col("file").endsWith(".pdf")

Utility Methods ​

alias() ​

Create an aliased expression (for renaming in aggregations).

typescript
alias(name: string): AliasExpr

Example:

typescript
// In aggregation context
df.groupBy("category", [
  { name: "total", expr: col("amount").sum().alias("total_amount") }
])

cast() ​

Cast to a different type.

typescript
cast(targetDType: DTypeKind): CastExpr

Example:

typescript
import { DTypeKind } from "molniya";

col("id").cast(DTypeKind.Int64)
col("price").cast(DTypeKind.Float64)

toExpr() ​

Get the underlying expression (rarely needed directly).

typescript
toExpr(): ColumnExpr

Example:

typescript
const expr = col("id").toExpr();

Chaining Examples ​

Complex Filter ​

typescript
df.filter(
  col("age")
    .gte(18)
    .and(col("age").lt(65))
    .and(col("active").eq(true))
)

Calculated Column ​

typescript
df.withColumn(
  "discounted_total",
  col("price")
    .mul(col("quantity"))
    .mul(col("discount"))
    .add(col("tax"))
)

String Matching ​

typescript
df.filter(
  col("email")
    .contains("@")
    .and(col("email").endsWith(".com"))
)

Method Equivalents ​

ColumnRef methods have equivalent standalone functions:

typescript
// These are equivalent:
col("a").add(col("b"))
add(col("a"), col("b"))

// These are equivalent:
col("a").gt(5)
gt(col("a"), 5)

Use whichever style you prefer. The ColumnRef methods are often more readable for chaining.