arquero/src/table/columns-from.js

Query processing and transformation of array-backed data tables.

import { error } from '../util/error.js';
import { isArray } from '../util/is-array.js';
import { isDate } from '../util/is-date.js';
import { isFunction } from '../util/is-function.js';
import { isObject } from '../util/is-object.js';
import { isRegExp } from '../util/is-regexp.js';
import { isString } from '../util/is-string.js';

/**
 * @return {import('./types.js').ColumnData}
 */
export function columnsFrom(values, names) {
  const raise = type => error(`Illegal argument type: ${type || typeof values}`);
  // @ts-ignore
  return values instanceof Map ? fromKeyValuePairs(values.entries(), names)
    : isDate(values) ? raise('Date')
    : isRegExp(values) ? raise('RegExp')
    : isString(values) ? raise()
    : isArray(values) ? fromArray(values, names)
    : isFunction(values[Symbol.iterator]) ? fromIterable(values, names)
    : isObject(values) ? fromKeyValuePairs(Object.entries(values), names)
    : raise();
}

function fromKeyValuePairs(entries, names = ['key', 'value']) {
  const keys = [];
  const vals = [];

  for (const [key, val] of entries) {
    keys.push(key);
    vals.push(val);
  }

  const columns = {};
  if (names[0]) columns[names[0]] = keys;
  if (names[1]) columns[names[1]] = vals;
  return columns;
}

function fromArray(values, names) {
  const len = values.length;
  const columns = {};
  const add = name => columns[name] = Array(len);

  if (len) {
    names = names || Object.keys(values[0]);
    const cols = names.map(add);
    const n = cols.length;
    for (let idx = 0; idx < len; ++idx) {
      const row = values[idx];
      for (let i = 0; i < n; ++i) {
        cols[i][idx] = row[names[i]];
      }
    }
  } else if (names) {
    names.forEach(add);
  }

  return columns;
}

function fromIterable(values, names) {
  const columns = {};
  const add = name => columns[name] = [];

  let cols;
  let n;
  for (const row of values) {
    if (!cols) {
      names = names || Object.keys(row);
      cols = names.map(add);
      n = cols.length;
    }
    for (let i = 0; i < n; ++i) {
      cols[i].push(row[names[i]]);
    }
  }

  if (!cols && names) {
    names.forEach(add);
  }

  return columns;
}