API Reference

Complete reference for Molniya's public API.

Overview

Molniya's API is organized into several modules:

Module	Description
DataFrame	Core data structure and transformation methods
Expressions	Building blocks for filters, calculations, and aggregations
Data Types	Type system for schema definitions
I/O	Reading and writing data files
Operators	Low-level streaming operations
Visualization	Chart generation from DataFrames

Import Patterns

// Main exports - covers most use cases
import { 
  readCsv, readParquet, fromRecords, fromCsvString,
  DataFrame, DType, 
  col, lit, and, or, not,
  sum, avg, min, max, count, first, last,
  asc, desc
} from "molniya";

// Advanced: Direct access to operators
import { filter, project, aggregate, sort, limit } from "molniya";

// Advanced: Schema and types
import { createSchema, DTypeKind } from "molniya";

API Categories

DataFrame Operations

• DataFrame Class - Core class and properties
• Creation Functions - readCsv, fromRecords, etc.
• Inspection Methods - show, count, schema
• Execution Methods - collect, toArray, toChunks

Transformations

• Filtering - filter, where
• Projection - select, drop, rename
• Column Operations - withColumn, cast, fillNull
• Sorting & Limiting - sort, limit, head, slice

Aggregation & Joins

• GroupBy - Grouping and the RelationalGroupedDataset class
• Aggregation Functions - sum, avg, count, etc.
• Joins - innerJoin, leftJoin, crossJoin, etc.

Expressions

• Expression Builders - col, lit, arithmetic functions
• ColumnRef - Column reference methods
• Operators - Comparison and logical operators

Data Types

• DType - Data type factory
• DTypeKind - Type identifiers
• Schema - Schema creation and manipulation

I/O

• CSV - CSV reading options and functions
• Parquet - Parquet file support

Visualization

• Plotting - Bar, line, scatter, and histogram charts

TypeScript Types

Molniya exports several TypeScript types for advanced use:

import type { 
  DataFrame,
  Expr,
  ColumnRef,
  Schema,
  DType,
  DTypeKind,
  CsvOptions,
  CsvSchemaSpec,
  AggSpec,
  SortKey,
  JoinConfig
} from "molniya";

Error Handling

Most API methods throw descriptive errors for invalid operations:

try {
  const df = await readCsv("missing.csv", schema);
} catch (error) {
  // Error: File not found or unreadable
}

try {
  df.filter(col("nonexistent").gt(0));
} catch (error) {
  // Error: Column not found
}

Version Compatibility

This documentation covers Molniya v0.1.0. The API is subject to change while in pre-1.0 development.

See Also

• Getting Started Guide - Introduction to concepts
• Cookbook - Practical usage patterns
• Examples - Real-world scenarios