210 lines
4.5 KiB
Markdown
210 lines
4.5 KiB
Markdown
---
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id: 5e4ce2bbac708cc68c1df25f
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title: Letter frequency
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challengeType: 5
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forumTopicId: 385263
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dashedName: letter-frequency
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---
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# --description--
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Given a string, calculate the frequency of each character.
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All characters should be counted. This includes lower and upper case letters, digits, whitespace, special characters, or any other distinct characters.
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# --instructions--
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Write a function to count the occurrences of each character in a given string.
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The function should return a 2D array with each of the elements in the following form: `['char', freq]`. The character should be a string with a length of 1, and frequency is a number denoting the count.
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For example, given the string "ab", your function should return `[['a', 1], ['b', 1]]`.
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# --hints--
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`letterFrequency` should be a function.
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```js
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assert(typeof letterFrequency == 'function');
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```
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`letterFrequency("Not all that Mrs. Bennet, however")` should return an array.
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```js
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assert(Array.isArray(letterFrequency('Not all that Mrs. Bennet, however')));
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```
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`letterFrequency("Not all that Mrs. Bennet, however")` should return `[[" ", 5], [",", 1], [".", 1], ["B", 1], ["M", 1], ["N", 1], ["a", 2], ["e", 4], ["h", 2], ["l", 2], ["n", 2], ["o", 2], ["r", 2], ["s", 1], ["t", 4], ["v", 1], ["w", 1]]`.
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```js
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assert.deepEqual(letterFrequency('Not all that Mrs. Bennet, however'), [
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[' ', 5],
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[',', 1],
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['.', 1],
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['B', 1],
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['M', 1],
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['N', 1],
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['a', 2],
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['e', 4],
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['h', 2],
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['l', 2],
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['n', 2],
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['o', 2],
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['r', 2],
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['s', 1],
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['t', 4],
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['v', 1],
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['w', 1]
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]);
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```
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`letterFrequency("daughters, could ask on the ")` should return `[[" ", 5],[",", 1],["a", 2],["c", 1],["d", 2],["e", 2],["g", 1],["h", 2],["k", 1],["l", 1],["n", 1],["o", 2],["r", 1],["s", 2],["t", 2],["u", 2]]`.
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```js
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assert.deepEqual(letterFrequency('daughters, could ask on the '), [
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[' ', 5],
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[',', 1],
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['a', 2],
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['c', 1],
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['d', 2],
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['e', 2],
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['g', 1],
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['h', 2],
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['k', 1],
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['l', 1],
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['n', 1],
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['o', 2],
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['r', 1],
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['s', 2],
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['t', 2],
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['u', 2]
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]);
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```
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`letterFrequency("husband any satisfactory description")` should return `[[" ", 3], ["a", 4], ["b", 1], ["c", 2], ["d", 2], ["e", 1], ["f", 1], ["h", 1], ["i", 3], ["n", 3], ["o", 2], ["p", 1], ["r", 2], ["s", 4], ["t", 3], ["u", 1], ["y", 2]]`.
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```js
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assert.deepEqual(letterFrequency('husband any satisfactory description'), [
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[' ', 3],
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['a', 4],
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['b', 1],
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['c', 2],
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['d', 2],
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['e', 1],
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['f', 1],
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['h', 1],
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['i', 3],
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['n', 3],
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['o', 2],
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['p', 1],
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['r', 2],
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['s', 4],
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['t', 3],
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['u', 1],
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['y', 2]
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]);
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```
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`letterFrequency("in various ways--with barefaced")` should return `[[" ", 3], ["-", 2], ["a", 4], ["b", 1], ["c", 1], ["d", 1], ["e", 2], ["f", 1], ["h", 1], ["i", 3], ["n", 1], ["o", 1], ["r", 2], ["s", 2], ["t", 1], ["u", 1], ["v", 1], ["w", 2], ["y", 1]]`.
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```js
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assert.deepEqual(letterFrequency('in various ways--with barefaced'), [
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[' ', 3],
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['-', 2],
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['a', 4],
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['b', 1],
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['c', 1],
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['d', 1],
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['e', 2],
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['f', 1],
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['h', 1],
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['i', 3],
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['n', 1],
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['o', 1],
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['r', 2],
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['s', 2],
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['t', 1],
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['u', 1],
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['v', 1],
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['w', 2],
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['y', 1]
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]);
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```
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`letterFrequency("distant surmises; but he eluded")` should return `[[" ", 4], [";", 1], ["a", 1], ["b", 1], ["d", 3], ["e", 4], ["h", 1], ["i", 2], ["l", 1], ["m", 1], ["n", 1], ["r", 1], ["s", 4], ["t", 3], ["u", 3]]`.
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```js
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assert.deepEqual(letterFrequency('distant surmises; but he eluded'), [
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[' ', 4],
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[';', 1],
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['a', 1],
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['b', 1],
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['d', 3],
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['e', 4],
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['h', 1],
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['i', 2],
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['l', 1],
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['m', 1],
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['n', 1],
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['r', 1],
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['s', 4],
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['t', 3],
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['u', 3]
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]);
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```
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`letterFrequency("last obliged to accept the second-hand,")` should return `[[" ", 5], [",", 1], ["-", 1], ["a", 3], ["b", 1], ["c", 3], ["d", 3], ["e", 4], ["g", 1], ["h", 2], ["i", 1], ["l", 2], ["n", 2], ["o", 3], ["p", 1], ["s", 2], ["t", 4]]`.
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```js
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assert.deepEqual(letterFrequency('last obliged to accept the second-hand,'), [
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[' ', 5],
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[',', 1],
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['-', 1],
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['a', 3],
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['b', 1],
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['c', 3],
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['d', 3],
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['e', 4],
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['g', 1],
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['h', 2],
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['i', 1],
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['l', 2],
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['n', 2],
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['o', 3],
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['p', 1],
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['s', 2],
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['t', 4]
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]);
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```
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# --seed--
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## --seed-contents--
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```js
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function letterFrequency(txt) {
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}
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```
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# --solutions--
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```js
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function letterFrequency(txt) {
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var cs = txt.split(''),
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i = cs.length,
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dct = {},
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c = '',
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keys;
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while (i--) {
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c = cs[i];
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dct[c] = (dct[c] || 0) + 1;
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}
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keys = Object.keys(dct);
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keys.sort();
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return keys.map(function (c) { return [c, dct[c]]; });
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}
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```
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