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Rails Migration

http://guides.rubyonrails.org/migrations.html

Migrations methods:

• add_column
• add_index
• change_column
• change_table
• create_table
• drop_table

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const http = require('http');
const url = require('url');
const fs = require('fs');
const path = require('path');
const port = process.argv[2] || 9000;

http.createServer(function (req, res) {
  console.log(`${req.method} ${req.url}`);

  // parse URL

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#=== Real life examples ===

graph = RDF::Graph.new
# read from file
graph = RDF::Graph.load("http://datagraph.org/jhacker/foaf.nt")
# -or- from the web
graph = RDF::Graph.load("http://dbpedia.org/resource/Elvis_Presley")
graph << RDF::RDFa::Reader.open("http://www.bestbuy.com/shop/ipad+xoom+-windows")

graph.each_predicate { |s| puts s.inspect }

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Rails ActiveRecord (association) - Cheatsheet

http://guides.rubyonrails.org/association_basics.html

Types of associations

• belongs_to : TABLE_NAME
• has_one : TABLE_NAME [:through => :TABLE_NAME]
• has_many : TABLE_NAME [:through => :TABLE_NAME]
• has_and_belongs_to_many : TABLE_NAME [:join_table => :TABLE_NAME]

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tmux shortcuts & cheatsheet v1.1.0

start new:

tmux

start new with session name:

tmux new -s myname

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The introduction to Reactive Programming you've been missing

(by @andrestaltz)

---

This tutorial as a series of videos

If you prefer to watch video tutorials with live-coding, then check out this series I recorded with the same contents as in this article: Egghead.io - Introduction to Reactive Programming.

---

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time node ./lib/permutations.js
# getPermutations('abcdefghij') // => abcdefghij, abcdefghji, abcdefgihj, abcdefgijh, abcdefgjhi, abcdefgjih, abcdefhgij...
# // n = 10, f(n) = 3,628,800;
# ./lib/permutations.js  8.06s user 0.63s system 101% cpu 8.562 total

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getPermutations('ab') // ab, ba...
// n = 2, f(n) = 2;
getPermutations('abc') // abc, acb, bac, bca, cab, cba...
// n = 3, f(n) = 6;
getPermutations('abcd') // abcd, abdc, acbd, acdb, adbc, adcb, bacd...
// n = 4, f(n) = 24;
getPermutations('abcde') // abcde, abced, abdce, abdec, abecd, abedc, acbde...
// n = 5, f(n) = 120;

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function getPermutations(string, prefix = '') {
  if(string.length <= 1) {
    return [prefix + string];
  }

  return Array.from(string).reduce((result, char, index) => {
    const reminder = string.slice(0, index) + string.slice(index+1);
    result = result.concat(getPermutations(reminder, prefix + char));
    return result;
  }, []);

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getPermutations('a') // => [ 'a']
getPermutations('ab') // =>  [ 'ab', 'ba']
getPermutations('abc') // => [ 'abc', 'acb', 'bac', 'bca', 'cab', 'cba' ]