Bootstrap 4 - Column to row on small display

Question

Have a grid with 4 columns and 4 rows. What I want to happen is on a small display the 4th column becomes a 5th row on a small display vs the column that it is on a medium+ display. It's a pet project to try and understand the bootstrap grid layout better. I'm essentially making a responsive calculator for the practice. I feel like I could do this with just raw CSS but figured bootstrap had to have some utilities that would make this easier. Images for example.

Large format:

Small format:

I have a start for the markup. There is some more associated CSS but I don't think it's important in the example. I've had a few versions but this is where I'm at in the moment.

<div class="container">
  <div class="row">
    <div class="col-md-8">
      <div class="row">
        <button type="button" class="btn-lg btn-outline-dark">1</button>
        <button type="button" class="btn-lg btn-outline-dark">2</button>
        <button type="button" class="btn-lg btn-outline-dark">3</button>
      </div>
      <div class="row">
        <button type="button" class="btn-lg btn-outline-dark">4</button>
        <button type="button" class="btn-lg btn-outline-dark">5</button>
        <button type="button" class="btn-lg btn-outline-dark">6</button>
      </div>
      <div class="row">
        <button type="button" class="btn-lg btn-outline-dark">7</button>
        <button type="button" class="btn-lg btn-outline-dark">8</button>
        <button type="button" class="btn-lg btn-outline-dark">9</button>
      </div>
      <div class="row">
        <button type="button" class="btn-lg btn-outline-light">&plusmn;</button>
        <button type="button" class="btn-lg btn-outline-dark">0</button>
        <button type="button" class="btn-lg btn-outline-light">.</button>
      </div>
    </div>
    <div class="col-md-4">
      <div class="row">
        <button type="button" class="btn-lg btn-outline-dark">X</button>
      </div>
      <div class="row">
        <button type="button" class="btn-lg btn-outline-dark">-</button>
      </div>
      <div class="row">
        <button type="button" class="btn-lg btn-outline-dark">+</button>
      </div>
      <div class="row">
        <button type="button" class="btn-lg btn-outline-dark">=</button>
      </div>
    </div>
  </div>
</div>

EDIT: I can only pick one solution as an answer but kiranvj, WebDevBooster, and dferenc all provided Bootstrap 4 release version working solutions. I can only mark one as an answer. No slight to the rest of you guys. My hands are tied.

Answer 1

I would do something like this. Check in full screen mode and resize to small

<link href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" rel="stylesheet"/>
<div class="row text-center">
  <div class="col-12 col-sm-8">
    <div class="row">
      <div class="col-4">black</div>
      <div class="col-4">black</div>
      <div class="col-4">black</div>
    </div>
    <div class="row">
      <div class="col-4">black</div>
      <div class="col-4">black</div>
      <div class="col-4">black</div>
    </div>
    <div class="row">
      <div class="col-4">black</div>
      <div class="col-4">black</div>
      <div class="col-4">black</div>
    </div>
  </div>
  <div class="col-12 col-sm-4 text-danger">
    <div class="row">
      	<div class="col-4 col-sm-12">pink</div>
      	<div class="col-4 col-sm-12">pink</div>
      	<div class="col-4 col-sm-12">pink</div>
    </div>
  </div>
</div>

Answer 2

I think, the simplest possible markup is the one below. It also uses the Order classes, but instead of setting the order of every button explicitly, this one touches just the "extra" buttons in the last column with .order-last .order-sm-0.

<div class="container">
    <div class="row justify-content-center">
        <button type="button" class="col-4 col-sm-3 btn-lg btn-dark">1</button>
        <button type="button" class="col-4 col-sm-3 btn-lg btn-dark">2</button>
        <button type="button" class="col-4 col-sm-3 btn-lg btn-dark">3</button>

        <button type="button" class="col-4 col-sm-3 order-last order-sm-0 btn-lg btn-secondary">X</button>

        <button type="button" class="col-4 col-sm-3 btn-lg btn-dark">4</button>
        <button type="button" class="col-4 col-sm-3 btn-lg btn-dark">5</button>
        <button type="button" class="col-4 col-sm-3 btn-lg btn-dark">6</button>

        <button type="button" class="col-4 col-sm-3 order-last order-sm-0 btn-lg btn-secondary">-</button>

        <button type="button" class="col-4 col-sm-3 btn-lg btn-dark">7</button>
        <button type="button" class="col-4 col-sm-3 btn-lg btn-dark">8</button>
        <button type="button" class="col-4 col-sm-3 btn-lg btn-dark">9</button>

        <button type="button" class="col-4 col-sm-3 order-last order-sm-0 btn-lg btn-secondary">+</button>

        <button type="button" class="col-4 col-sm-3 btn-lg btn-dark">&plusmn;</button>
        <button type="button" class="col-4 col-sm-3 btn-lg btn-dark">0</button>
        <button type="button" class="col-4 col-sm-3 btn-lg btn-dark">.</button>
        
        <!--
        Use `col-12 col-sm-3` in case you want a full-width `=` button 
        In that case you could omit `.justify-content-center` at the wrapper
        -->
        <button type="button" class="col-12 col-sm-3 order-last order-sm-0 btn-lg btn-secondary">=</button>
    </div>
</div>


<link href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" rel="stylesheet"/>

Answer 3

What I would do is create 3 additional pink div elements that render below the black divs, and then hide them using the hidden-*-up and hidden-*-down classes. When the screen is small, hide the pink divs on the right and show the pink divs on the bottom, and vice versa when the screen is small.