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table.js
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table.js
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import {greatest, reverse} from "d3-array";
import {FileAttachment} from "./fileAttachment.js";
import {isArqueroTable} from "./arquero.js";
import {isArrowTable, loadArrow} from "./arrow.js";
import {DuckDBClient} from "./duckdb.js";
const nChecks = 20; // number of values to check in each array
// We support two levels of DatabaseClient. The simplest DatabaseClient
// implements only the client.sql tagged template literal. More advanced
// DatabaseClients implement client.query and client.queryStream, which support
// streaming and abort, and the client.queryTag tagged template literal is used
// to translate the contents of a SQL cell or Table cell into the appropriate
// arguments for calling client.query or client.queryStream. For table cells, we
// additionally require client.describeColumns. The client.describeTables method
// is optional.
export function isDatabaseClient(value, mode) {
return (
value &&
(typeof value.sql === "function" ||
(typeof value.queryTag === "function" &&
(typeof value.query === "function" ||
typeof value.queryStream === "function"))) &&
(mode !== "table" || typeof value.describeColumns === "function") &&
value !== __query // don’t match our internal helper
);
}
// Returns true if the value is a typed array (for a single-column table), or if
// it’s an array. In the latter case, the elements of the array must be
// consistently typed: either plain objects or primitives or dates.
export function isDataArray(value) {
return (
(Array.isArray(value) &&
(isQueryResultSetSchema(value.schema) ||
isQueryResultSetColumns(value.columns) ||
arrayContainsObjects(value) ||
arrayContainsPrimitives(value) ||
arrayContainsDates(value))) ||
isTypedArray(value)
);
}
// Given an array, checks that the given value is an array that does not contain
// any primitive values (at least for the first few values that we check), and
// that the first object contains enumerable keys (see computeSchema for how we
// infer the columns). We assume that the contents of the table are homogenous,
// but we don’t currently enforce this.
// https://observablehq.com/@observablehq/database-client-specification#§1
function arrayContainsObjects(value) {
const n = Math.min(nChecks, value.length);
for (let i = 0; i < n; ++i) {
const v = value[i];
if (v === null || typeof v !== "object") return false;
}
return n > 0 && objectHasEnumerableKeys(value[0]);
}
// Using a for-in loop here means that we can abort after finding at least one
// enumerable key (whereas Object.keys would require materializing the array of
// all keys, which would be considerably slower if the value has many keys!).
// This function assumes that value is an object; see arrayContainsObjects.
function objectHasEnumerableKeys(value) {
for (const _ in value) return true;
return false;
}
function isQueryResultSetSchema(schemas) {
return (
Array.isArray(schemas) &&
schemas.every(isColumnSchema)
);
}
function isQueryResultSetColumns(columns) {
return (Array.isArray(columns) && columns.every((name) => typeof name === "string"));
}
function isColumnSchema(schema) {
return schema && typeof schema.name === "string" && typeof schema.type === "string";
}
// Returns true if the value represents an array of primitives (i.e., a
// single-column table). This should only be passed values for which
// isDataArray returns true.
export function arrayIsPrimitive(value) {
return (
isTypedArray(value) ||
arrayContainsPrimitives(value) ||
arrayContainsDates(value)
);
}
// Given an array, checks that the first n elements are primitives (number,
// string, boolean, bigint) of a consistent type.
function arrayContainsPrimitives(value) {
const n = Math.min(nChecks, value.length);
if (!(n > 0)) return false;
let type;
let hasPrimitive = false; // ensure we encounter 1+ primitives
for (let i = 0; i < n; ++i) {
const v = value[i];
if (v == null) continue; // ignore null and undefined
const t = typeof v;
if (type === undefined) {
switch (t) {
case "number":
case "boolean":
case "string":
case "bigint":
type = t;
break;
default:
return false;
}
} else if (t !== type) {
return false;
}
hasPrimitive = true;
}
return hasPrimitive;
}
// Given an array, checks that the first n elements are dates.
function arrayContainsDates(value) {
const n = Math.min(nChecks, value.length);
if (!(n > 0)) return false;
let hasDate = false; // ensure we encounter 1+ dates
for (let i = 0; i < n; ++i) {
const v = value[i];
if (v == null) continue; // ignore null and undefined
if (!(v instanceof Date)) return false;
hasDate = true;
}
return hasDate;
}
function isTypedArray(value) {
return (
value instanceof Int8Array ||
value instanceof Int16Array ||
value instanceof Int32Array ||
value instanceof Uint8Array ||
value instanceof Uint8ClampedArray ||
value instanceof Uint16Array ||
value instanceof Uint32Array ||
value instanceof Float32Array ||
value instanceof Float64Array
);
}
// __query is used by table cells; __query.sql is used by SQL cells.
export const __query = Object.assign(
async (source, operations, invalidation, name) => {
source = await loadTableDataSource(await source, name);
if (isDatabaseClient(source)) return evaluateQuery(source, makeQueryTemplate(operations, source), invalidation);
if (isDataArray(source)) return __table(source, operations);
if (!source) throw new Error("missing data source");
throw new Error("invalid data source");
},
{
sql(source, invalidation, name) {
return async function () {
return evaluateQuery(await loadSqlDataSource(await source, name), arguments, invalidation);
};
}
}
);
export async function loadDataSource(source, mode, name) {
switch (mode) {
case "chart": return loadChartDataSource(source);
case "table": return loadTableDataSource(source, name);
case "sql": return loadSqlDataSource(source, name);
}
return source;
}
// We use a weak map to cache loaded data sources by key so that we don’t have
// to e.g. create separate SQLiteDatabaseClients every time we’re querying the
// same SQLite file attachment. Since this is a weak map, unused references will
// be garbage collected when they are no longer desired. Note: the name should
// be consistent, as it is not part of the cache key!
function sourceCache(loadSource) {
const cache = new WeakMap();
return (source, name) => {
if (!source || typeof source !== "object") throw new Error("invalid data source");
let promise = cache.get(source);
if (!promise || (isDataArray(source) && source.length !== promise._numRows)) {
// Warning: do not await here! We need to populate the cache synchronously.
promise = loadSource(source, name);
promise._numRows = source.length; // This will be undefined for DatabaseClients
cache.set(source, promise);
}
return promise;
};
}
const loadChartDataSource = sourceCache(async (source) => {
if (source instanceof FileAttachment) {
switch (source.mimeType) {
case "text/csv": return source.csv({typed: "auto"});
case "text/tab-separated-values": return source.tsv({typed: "auto"});
case "application/json": return source.json();
}
throw new Error(`unsupported file type: ${source.mimeType}`);
}
return source;
});
const loadTableDataSource = sourceCache(async (source, name) => {
if (source instanceof FileAttachment) {
switch (source.mimeType) {
case "text/csv": return source.csv();
case "text/tab-separated-values": return source.tsv();
case "application/json": return source.json();
case "application/x-sqlite3": return source.sqlite();
}
if (/\.(arrow|parquet)$/i.test(source.name)) return loadDuckDBClient(source, name);
throw new Error(`unsupported file type: ${source.mimeType}`);
}
if (isArrowTable(source) || isArqueroTable(source)) return loadDuckDBClient(source, name);
if (isDataArray(source) && arrayIsPrimitive(source))
return Array.from(source, (value) => ({value}));
return source;
});
const loadSqlDataSource = sourceCache(async (source, name) => {
if (source instanceof FileAttachment) {
switch (source.mimeType) {
case "text/csv":
case "text/tab-separated-values":
case "application/json": return loadDuckDBClient(source, name);
case "application/x-sqlite3": return source.sqlite();
}
if (/\.(arrow|parquet)$/i.test(source.name)) return loadDuckDBClient(source, name);
throw new Error(`unsupported file type: ${source.mimeType}`);
}
if (isDataArray(source)) return loadDuckDBClient(await asArrowTable(source, name), name);
if (isArrowTable(source) || isArqueroTable(source)) return loadDuckDBClient(source, name);
return source;
});
async function asArrowTable(array, name) {
const arrow = await loadArrow();
return arrayIsPrimitive(array)
? arrow.tableFromArrays({[name]: array})
: arrow.tableFromJSON(array);
}
function loadDuckDBClient(
source,
name = source instanceof FileAttachment
? getFileSourceName(source)
: "__table"
) {
return DuckDBClient.of({[name]: source});
}
function getFileSourceName(file) {
return file.name
.replace(/@\d+(?=\.|$)/, "") // strip Observable file version number
.replace(/\.\w+$/, ""); // strip file extension
}
async function evaluateQuery(source, args, invalidation) {
if (!source) throw new Error("missing data source");
// If this DatabaseClient supports abort and streaming, use that.
if (typeof source.queryTag === "function") {
const abortController = new AbortController();
const options = {signal: abortController.signal};
invalidation.then(() => abortController.abort("invalidated"));
if (typeof source.queryStream === "function") {
return accumulateQuery(
source.queryStream(...source.queryTag.apply(source, args), options)
);
}
if (typeof source.query === "function") {
return source.query(...source.queryTag.apply(source, args), options);
}
}
// Otherwise, fallback to the basic sql tagged template literal.
if (typeof source.sql === "function") {
return source.sql.apply(source, args);
}
// TODO: test if source is a file attachment, and support CSV etc.
throw new Error("source does not implement query, queryStream, or sql");
}
// Generator function that yields accumulated query results client.queryStream
async function* accumulateQuery(queryRequest) {
let then = performance.now();
const queryResponse = await queryRequest;
const values = [];
values.done = false;
values.error = null;
values.schema = queryResponse.schema;
try {
for await (const rows of queryResponse.readRows()) {
if (performance.now() - then > 150 && values.length > 0) {
yield values;
then = performance.now();
}
for (const value of rows) {
values.push(value);
}
}
values.done = true;
yield values;
} catch (error) {
values.error = error;
yield values;
}
}
/**
* Returns a SQL query in the form [[parts], ...params] where parts is an array
* of sub-strings and params are the parameter values to be inserted between each
* sub-string.
*/
export function makeQueryTemplate(operations, source) {
const escaper =
typeof source.escape === "function" ? source.escape : (i) => i;
const {select, from, filter, sort, slice} = operations;
if (!from.table)
throw new Error("missing from table");
if (select.columns && select.columns.length === 0)
throw new Error("at least one column must be selected");
const names = new Map(operations.names?.map(({column, name}) => [column, name]));
const columns = select.columns ? select.columns.map((column) => {
const override = names.get(column);
return override ? `${escaper(column)} AS ${escaper(override)}` : escaper(column);
}).join(", ") : "*";
const args = [
[`SELECT ${columns} FROM ${formatTable(from.table, escaper)}`]
];
for (let i = 0; i < filter.length; ++i) {
appendSql(i ? `\nAND ` : `\nWHERE `, args);
appendWhereEntry(filter[i], args, escaper);
}
for (let i = 0; i < sort.length; ++i) {
appendSql(i ? `, ` : `\nORDER BY `, args);
appendOrderBy(sort[i], args, escaper);
}
if (source.dialect === "mssql" || source.dialect === "oracle") {
if (slice.to !== null || slice.from !== null) {
if (!sort.length) {
if (!select.columns)
throw new Error(
"at least one column must be explicitly specified. Received '*'."
);
appendSql(`\nORDER BY `, args);
appendOrderBy(
{column: select.columns[0], direction: "ASC"},
args,
escaper
);
}
appendSql(`\nOFFSET ${slice.from || 0} ROWS`, args);
appendSql(
`\nFETCH NEXT ${
slice.to !== null ? slice.to - (slice.from || 0) : 1e9
} ROWS ONLY`,
args
);
}
} else {
if (slice.to !== null || slice.from !== null) {
appendSql(
`\nLIMIT ${slice.to !== null ? slice.to - (slice.from || 0) : 1e9}`,
args
);
}
if (slice.from !== null) {
appendSql(` OFFSET ${slice.from}`, args);
}
}
return args;
}
function formatTable(table, escaper) {
if (typeof table === "object") { // i.e., not a bare string specifier
let from = "";
if (table.database != null) from += escaper(table.database) + ".";
if (table.schema != null) from += escaper(table.schema) + ".";
from += escaper(table.table);
return from;
} else {
return escaper(table);
}
}
function appendSql(sql, args) {
const strings = args[0];
strings[strings.length - 1] += sql;
}
function appendOrderBy({column, direction}, args, escaper) {
appendSql(`${escaper(column)} ${direction.toUpperCase()}`, args);
}
function appendWhereEntry({type, operands}, args, escaper) {
if (operands.length < 1) throw new Error("Invalid operand length");
// Unary operations
// We treat `v` and `nv` as `NULL` and `NOT NULL` unary operations in SQL,
// since the database already validates column types.
if (operands.length === 1 || type === "v" || type === "nv") {
appendOperand(operands[0], args, escaper);
switch (type) {
case "n":
case "nv":
appendSql(` IS NULL`, args);
return;
case "nn":
case "v":
appendSql(` IS NOT NULL`, args);
return;
default:
throw new Error("Invalid filter operation");
}
}
// Binary operations
if (operands.length === 2) {
if (["in", "nin"].includes(type)) {
// Fallthrough to next parent block.
} else if (["c", "nc"].includes(type)) {
// TODO: Case (in)sensitive?
appendOperand(operands[0], args, escaper);
switch (type) {
case "c":
appendSql(` LIKE `, args);
break;
case "nc":
appendSql(` NOT LIKE `, args);
break;
}
appendOperand(likeOperand(operands[1]), args, escaper);
return;
} else {
appendOperand(operands[0], args, escaper);
switch (type) {
case "eq":
appendSql(` = `, args);
break;
case "ne":
appendSql(` <> `, args);
break;
case "gt":
appendSql(` > `, args);
break;
case "lt":
appendSql(` < `, args);
break;
case "gte":
appendSql(` >= `, args);
break;
case "lte":
appendSql(` <= `, args);
break;
default:
throw new Error("Invalid filter operation");
}
appendOperand(operands[1], args, escaper);
return;
}
}
// List operations
appendOperand(operands[0], args, escaper);
switch (type) {
case "in":
appendSql(` IN (`, args);
break;
case "nin":
appendSql(` NOT IN (`, args);
break;
default:
throw new Error("Invalid filter operation");
}
appendListOperands(operands.slice(1), args);
appendSql(")", args);
}
function appendOperand(o, args, escaper) {
if (o.type === "column") {
appendSql(escaper(o.value), args);
} else {
args.push(o.value);
args[0].push("");
}
}
// TODO: Support column operands here?
function appendListOperands(ops, args) {
let first = true;
for (const op of ops) {
if (first) first = false;
else appendSql(",", args);
args.push(op.value);
args[0].push("");
}
}
function likeOperand(operand) {
return {...operand, value: `%${operand.value}%`};
}
// Comparator function that moves null values (undefined, null, NaN) to the
// end of the array.
function defined(a, b) {
return (a == null || !(a >= a)) - (b == null || !(b >= b));
}
// Comparator function that sorts values in ascending order, with null values at
// the end.
function ascendingDefined(a, b) {
return defined(a, b) || (a < b ? -1 : a > b ? 1 : 0);
}
// Comparator function that sorts values in descending order, with null values
// at the end.
function descendingDefined(a, b) {
return defined(a, b) || (a > b ? -1 : a < b ? 1 : 0);
}
// Functions for checking type validity
const isValidNumber = (value) => typeof value === "number" && !Number.isNaN(value);
const isValidInteger = (value) => Number.isInteger(value) && !Number.isNaN(value);
const isValidString = (value) => typeof value === "string";
const isValidBoolean = (value) => typeof value === "boolean";
const isValidBigint = (value) => typeof value === "bigint";
const isValidDate = (value) => value instanceof Date && !isNaN(value);
const isValidBuffer = (value) => value instanceof ArrayBuffer;
const isValidArray = (value) => Array.isArray(value);
const isValidObject = (value) => typeof value === "object" && value !== null;
const isValidOther = (value) => value != null;
// Function to get the correct validity checking function based on type
export function getTypeValidator(colType) {
switch (colType) {
case "string":
return isValidString;
case "bigint":
return isValidBigint;
case "boolean":
return isValidBoolean;
case "number":
return isValidNumber;
case "integer":
return isValidInteger;
case "date":
return isValidDate;
case "buffer":
return isValidBuffer;
case "array":
return isValidArray;
case "object":
return isValidObject;
case "other":
default:
return isValidOther;
}
}
// Accepts dates in the form of ISOString and LocaleDateString, with or without time
const DATE_TEST = /^(([-+]\d{2})?\d{4}(-\d{2}(-\d{2}))|(\d{1,2})\/(\d{1,2})\/(\d{2,4}))([T ]\d{2}:\d{2}(:\d{2}(\.\d{3})?)?(Z|[-+]\d{2}:\d{2})?)?$/;
export function coerceToType(value, type) {
switch (type) {
case "string":
return typeof value === "string" || value == null ? value : String(value);
case "boolean":
if (typeof value === "string") {
const trimValue = value.trim().toLowerCase();
return trimValue === "true"
? true
: trimValue === "false"
? false
: null;
}
return typeof value === "boolean" || value == null
? value
: Boolean(value);
case "bigint":
return typeof value === "bigint" || value == null
? value
: Number.isInteger(typeof value === "string" && !value.trim() ? NaN : +value)
? BigInt(value) // eslint-disable-line no-undef
: undefined;
case "integer": // not a target type for coercion, but can be inferred
case "number": {
return typeof value === "number"
? value
: value == null || (typeof value === "string" && !value.trim())
? NaN
: Number(value);
}
case "date": {
if (value instanceof Date || value == null) return value;
if (typeof value === "number") return new Date(value);
const trimValue = String(value).trim();
if (typeof value === "string" && !trimValue) return null;
return new Date(DATE_TEST.test(trimValue) ? trimValue : NaN);
}
case "array":
case "object":
case "buffer":
case "other":
return value;
default:
throw new Error(`Unable to coerce to type: ${type}`);
}
}
export function getSchema(source) {
const {columns} = source;
let {schema} = source;
if (!isQueryResultSetSchema(schema)) {
schema = inferSchema(source, isQueryResultSetColumns(columns) ? columns : undefined);
return {schema, inferred: true};
}
return {schema, inferred: false};
}
// This function infers a schema from the source data, if one doesn't already
// exist, and merges type assertions into that schema. If the schema was
// inferred or if there are type assertions, it then coerces the rows in the
// source data to the types specified in the schema.
function applyTypes(source, operations) {
const input = source;
let {schema, inferred} = getSchema(source);
const types = new Map(schema.map(({name, type}) => [name, type]));
if (operations.types) {
for (const {name, type} of operations.types) {
types.set(name, type);
// update schema with user-selected type
if (schema === input.schema) schema = schema.slice(); // copy on write
const colIndex = schema.findIndex((col) => col.name === name);
if (colIndex > -1) schema[colIndex] = {...schema[colIndex], type};
}
source = source.map(d => coerceRow(d, types, schema));
} else if (inferred) {
// Coerce data according to new schema, unless that happened due to
// operations.types, above.
source = source.map(d => coerceRow(d, types, schema));
}
return {source, schema};
}
function applyNames(source, operations) {
if (!operations.names) return source;
const overridesByName = new Map(operations.names.map((n) => [n.column, n]));
return source.map((d) =>
Object.fromEntries(Object.keys(d).map((k) => {
const override = overridesByName.get(k);
return [override?.name ?? k, d[k]];
}))
);
}
// This function applies table cell operations to an in-memory table (array of
// objects); it should be equivalent to the corresponding SQL query. TODO Use
// DuckDBClient for data arrays, too, and then we wouldn’t need our own __table
// function to do table operations on in-memory data?
export function __table(source, operations) {
const errors = new Map();
const input = source;
const typed = applyTypes(source, operations);
source = typed.source;
let schema = typed.schema;
if (operations.derive) {
// Derived columns may depend on coerced values from the original data source,
// so we must evaluate derivations after the initial inference and coercion
// step.
const derivedSource = [];
operations.derive.map(({name, value}) => {
let columnErrors = [];
// Derived column formulas may reference renamed columns, so we must
// compute derivations on the renamed source. However, we don't modify the
// source itself with renamed names until after the other operations are
// applied, because operations like filter and sort reference original
// column names.
// TODO Allow derived columns to reference other derived columns.
applyNames(source, operations).map((row, index) => {
let resolved;
try {
// TODO Support referencing `index` and `rows` in the derive function.
resolved = value(row);
} catch (error) {
columnErrors.push({index, error});
resolved = undefined;
}
if (derivedSource[index]) {
derivedSource[index] = {...derivedSource[index], [name]: resolved};
} else {
derivedSource.push({[name]: resolved});
}
});
if (columnErrors.length) errors.set(name, columnErrors);
});
// Since derived columns are untyped by default, we do a pass of type
// inference and coercion after computing the derived values.
const typedDerived = applyTypes(derivedSource, operations);
// Merge derived source and schema with the source dataset.
source = source.map((row, i) => ({...row, ...typedDerived.source[i]}));
schema = [...schema, ...typedDerived.schema];
}
for (const {type, operands} of operations.filter) {
const [{value: column}] = operands;
const values = operands.slice(1).map(({value}) => value);
switch (type) {
// valid (matches the column type)
case "v": {
const [colType] = values;
const isValid = getTypeValidator(colType);
source = source.filter(d => isValid(d[column]));
break;
}
// not valid (doesn't match the column type)
case "nv": {
const [colType] = values;
const isValid = getTypeValidator(colType);
source = source.filter(d => !isValid(d[column]));
break;
}
case "eq": {
const [value] = values;
if (value instanceof Date) {
const time = +value; // compare as primitive
source = source.filter((d) => +d[column] === time);
} else {
source = source.filter((d) => d[column] === value);
}
break;
}
case "ne": {
const [value] = values;
source = source.filter((d) => d[column] !== value);
break;
}
case "c": {
const [value] = values;
source = source.filter(
(d) => typeof d[column] === "string" && d[column].includes(value)
);
break;
}
case "nc": {
const [value] = values;
source = source.filter(
(d) => typeof d[column] === "string" && !d[column].includes(value)
);
break;
}
case "in": {
const set = new Set(values); // TODO support dates?
source = source.filter((d) => set.has(d[column]));
break;
}
case "nin": {
const set = new Set(values); // TODO support dates?
source = source.filter((d) => !set.has(d[column]));
break;
}
case "n": {
source = source.filter((d) => d[column] == null);
break;
}
case "nn": {
source = source.filter((d) => d[column] != null);
break;
}
case "lt": {
const [value] = values;
source = source.filter((d) => d[column] < value);
break;
}
case "lte": {
const [value] = values;
source = source.filter((d) => d[column] <= value);
break;
}
case "gt": {
const [value] = values;
source = source.filter((d) => d[column] > value);
break;
}
case "gte": {
const [value] = values;
source = source.filter((d) => d[column] >= value);
break;
}
default:
throw new Error(`unknown filter type: ${type}`);
}
}
for (const {column, direction} of reverse(operations.sort)) {
const compare = direction === "desc" ? descendingDefined : ascendingDefined;
if (source === input) source = source.slice(); // defensive copy
source.sort((a, b) => compare(a[column], b[column]));
}
let {from, to} = operations.slice;
from = from == null ? 0 : Math.max(0, from);
to = to == null ? Infinity : Math.max(0, to);
if (from > 0 || to < Infinity) {
source = source.slice(Math.max(0, from), Math.max(0, to));
}
// Preserve the schema for all columns.
let fullSchema = schema.slice();
if (operations.select.columns) {
if (schema) {
const schemaByName = new Map(schema.map((s) => [s.name, s]));
schema = operations.select.columns.map((c) => schemaByName.get(c));
}
source = source.map((d) =>
Object.fromEntries(operations.select.columns.map((c) => [c, d[c]]))
);
}
if (operations.names) {
const overridesByName = new Map(operations.names.map((n) => [n.column, n]));
if (schema) {
schema = schema.map((s) => {
const override = overridesByName.get(s.name);
return ({...s, ...(override ? {name: override.name} : null)});
});
}
if (fullSchema) {
fullSchema = fullSchema.map((s) => {
const override = overridesByName.get(s.name);
return ({...s, ...(override ? {name: override.name} : null)});
});
}
source = applyNames(source, operations);
}
if (source !== input) {
if (schema) source.schema = schema;
}
source.fullSchema = fullSchema;
source.errors = errors;
return source;
}
export function coerceRow(object, types, schema) {
const coerced = {};
for (const col of schema) {
const type = types.get(col.name);
const value = object[col.name];
coerced[col.name] = type === "raw" ? value : coerceToType(value, type);
}
return coerced;
}
function createTypeCount() {
return {
boolean: 0,
integer: 0,
number: 0,
date: 0,
string: 0,
array: 0,
object: 0,
bigint: 0,
buffer: 0,
defined: 0
};
}
// Caution: the order below matters! 🌶️ The first one that passes the ≥90% test
// should be the one that we chose, and therefore these types should be listed
// from most specific to least specific.
const types = [
"boolean",
"integer",
"number",
"date",
"bigint",
"array",
"object",
"buffer"
// Note: "other" and "string" are intentionally omitted; see below!
];
// We need to show *all* keys present in the array of Objects
function getAllKeys(rows) {
const keys = new Set();
for (const row of rows) {
// avoid crash if row is null or undefined
if (row) {
// only enumerable properties
for (const key in row) {
// only own properties
if (Object.prototype.hasOwnProperty.call(row, key)) {
// unique properties, in the order they appear
keys.add(key);
}
}
}
}
return Array.from(keys);
}
export function inferSchema(source, columns = getAllKeys(source)) {
const schema = [];
const sampleSize = 100;
const sample = source.slice(0, sampleSize);
const typeCounts = {};
for (const col of columns) {
const colCount = typeCounts[col] = createTypeCount();
for (const d of sample) {
let value = d[col];
if (value == null) continue;
const type = typeof value;
if (type !== "string") {
++colCount.defined;
if (Array.isArray(value)) ++colCount.array;
else if (value instanceof Date) ++colCount.date;
else if (value instanceof ArrayBuffer) ++colCount.buffer;
else if (type === "number") {
++colCount.number;
if (Number.isInteger(value)) ++colCount.integer;
}
// bigint, boolean, or object
else if (type in colCount) ++colCount[type];
} else {
value = value.trim();
if (!value) continue;
++colCount.defined;
++colCount.string;
if (/^(true|false)$/i.test(value)) {
++colCount.boolean;
} else if (value && !isNaN(value)) {
++colCount.number;
if (Number.isInteger(+value)) ++colCount.integer;
} else if (DATE_TEST.test(value)) ++colCount.date;
}
}
// Chose the non-string, non-other type with the greatest count that is also
// ≥90%; or if no such type meets that criterion, fallback to string if
// ≥90%; and lastly fallback to other.
const minCount = Math.max(1, colCount.defined * 0.9);
const type =
greatest(types, (type) =>
colCount[type] >= minCount ? colCount[type] : NaN
) ?? (colCount.string >= minCount ? "string" : "other");
schema.push({
name: col,
type: type,
inferred: type
});
}
return schema;
}