Edit in JSFiddle

var selectByGroup = function(groupName){
    $('input[name=' + groupName + ']').attr('checked', true); 
};

var selectByClass = function(className){
    $('input.' + className + '').attr('checked', true);
};

var reset = function(){
    $('input').attr('checked', false);
};

$('#btn1').click(function(){
    selectByGroup('group1');
});

$('#btn2').click(function(){
    selectByClass('check');
});

$('#btn-reset').click(function(){
    reset();
});

<h2>group 1</h2>
<label>one</label><input type="checkbox" name="group1" class="check"/>
<label>two</label><input type="checkbox" name="group1" class="check" />

<h2>group 2</h2>
<label>one</label><input type="checkbox" name="group2" class="check" />
<label>two</label><input type="checkbox" name="group2" class="check" />

<div id="tools">
<button id="btn1">select group1</button>
<button id="btn2">select all</button>

<button id="btn-reset">reset</button>
</div>

#tools {
    margin: 10px 0;
}