Scientific notation formatting

Co-authored-by: Phil DeOrsey <pdeorsey@amplify.com>
mathigon · Aug 20, 2023 · e107de8 · e107de8
1 parent 7bcc793
commit e107de8
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Showing 2 changed files with 29 additions and 1 deletion.
diff --git a/src/arithmetic.ts b/src/arithmetic.ts
@@ -72,6 +72,22 @@ export function numberFormat(n: number, places = 0, separators = true) {
   return separators ? addThousandSeparators(str) : str;
 }
 
+export function scientificFormat(value: number, places = 6) {
+  const abs = Math.abs(value);
+  if (isBetween(abs, Math.pow(10, -places), Math.pow(10, places))) {
+    return numberFormat(value, places);
+  }
+
+  // TODO Decide how we want to handle these special cases
+  if (abs > Number.MAX_VALUE) return `${Math.sign(value) < 0 ? '–' : ''}∞`;
+  if (abs < Number.MIN_VALUE) return '0';
+
+  const [str, exponent] = value.toExponential().split('e');
+  const top = exponent.replace('+', '').replace('-', '–');
+  const isNegative = top.startsWith('–');
+  return `${str.slice(0, 5)} × 10^${(isNegative ? '(' : '') + top + (isNegative ? ')' : '')}`;
+}
+
 // Numbers like 0,123 are decimals, even though they match POINT_DECIMAL.
 const SPECIAL_DECIMAL = /^-?0,[0-9]+$/;
 

diff --git a/test/arithmetic-test.ts b/test/arithmetic-test.ts
@@ -5,7 +5,7 @@
 
 
 import tape from 'tape';
-import {numberFormat, parseNumber, toWord} from '../src';
+import {numberFormat, parseNumber, scientificFormat, toWord} from '../src';
 
 
 tape('numberFormat', (test) => {
@@ -43,6 +43,18 @@ tape('numberFormat', (test) => {
   test.equal(numberFormat(0.001, 3), '0', ':: numberFormat(0.001, 3)');
   test.equal(numberFormat(-0.001, 5), '–0.001', ':: numberFormat(-0.001, 5)');
   test.equal(numberFormat(-0.001, 4), '0', ':: numberFormat(-0.001, 4)');
+
+  test.equal(scientificFormat(123123123, 6), '1.231 × 10^8');
+  test.equal(scientificFormat(123123, 6), '123,123');
+  test.equal(scientificFormat(-123123123, 6), '-1.23 × 10^8');
+
+  test.equal(scientificFormat(0.000123, 6), '0.00012');
+  test.equal(scientificFormat(0.000000123, 6), '1.23 × 10^(–7)');
+  test.equal(scientificFormat(-0.000000123, 6), '-1.23 × 10^(–7)');
+
+  test.equal(scientificFormat(-Number.MAX_VALUE * 10, 6), '–∞');
+  test.equal(scientificFormat(-Number.MIN_VALUE / 10, 6), '0');
+
   test.end();
 });