html layout: how to float divs vertically

Question

How do I get divs to float vertically like in this picture:

Background: I have a grid of checkboxes with content sorted alphabetically and I'd like to have alphabetic order progress vertically (since horizontal order is quite hard to follow). All the divs have same size (width like picture, height = 1 line size).

Update: To clarify: The main intention is to have a table layout with a variable amount of columns based on available screen width and have the cells in column-major order. The actual number of divs is not known in advance.

Answer 1

CSS

.cols {
        width:20%;
        float:left;
    }
    .rows {
        height:100px;
    }

HTML

 <div class="cols">
        <div class="rows">Div 1</div>
        <div class="rows">Div 2</div>
        <div class="rows">Div 3</div>
    </div>

    <div class="cols">
        <div class="rows">Div 4</div>
        <div class="rows">Div 5</div>
        <div class="rows">Div 6</div>
    </div>

    <div class="cols">
        <div class="rows">Div 7</div>
    </div>