Group-By-Count ESLint errors

count-lint-errors.js

// :: (String, String) => String
const spawn = require('child_process').spawnSync;

// :: String => [String]
const getRules = raw => raw
    .split('\n')
    .map(line => line.trim())
    .filter(line => !!line)
    .filter(line => line[0] !== '/' && line[0] !== '✖')
    .map(line => line.match(/[a-z-]+$/)[0]);

// :: [String] => Object
const groupByCount = list => {
    const dict = {};
    list.forEach(item => {
        dict[item] = dict[item] || 0;
        dict[item]++;
    });
    return dict;
};

// :: Object => [Object]
const sortByValue = dict => {
    const arr = [];
    for (const key in dict) {
        if (!dict.hasOwnProperty(key)) continue;
        arr.push([key, dict[key]]);
    }
    arr.sort((a, b) => a[1] < b[1] ? 1 : a[1] > b[1] ? -1 : 0);
    return arr;
};

// :: String => [String]
const app = str => sortByValue(groupByCount(getRules(str)));

const output = spawn('eslint', ['.'], {encoding: 'utf8'}).stdout;
console.log(app(output));

count-lint-errors.sh

eslint . | grep -v "^[\/✖]" | grep -v '^$' | perl -ne 's/(?:.+) ([\w-]+$)/$1/g; print;' | sort | uniq -c | sort

count-lint-errors.sh does not identify the following lines as identical warnings (perhaps because of the quotes):

P.S. Very nice command though!!

it is because of the / in type of error.
Updated script:
eslint . | grep -v "^[\/✖]" | grep -v '^$' | perl -ne 's/(?:.+) ([\/\w-]+$)/$1/g; print;' | sort | uniq -c | sort

If your package name has @ in it, use this instead:

 % cat linter-output.txt | grep -v "^[\/✖]"  | grep -v '^$' | perl -ne 's/(?:.+) ([@\/\w-]+$)/$1/g; print;' | sort | uniq -c | sort

Very useful script, thanks a lot!