// FUNCTION: shows/hides appropriate divs
function getCategory(cat) {

  // show all elements
  if(cat == "all") {
    var imgArray = document.getElementsByTagName("a");
    for(i = 0; i < imgArray.length; i++) {
      if(imgArray[i].className.length > 0) {
        imgArray[i].style.display = "inline";
      }
    }
  }
  
  // get all image elements
  else if(cat != "all") {
    var imgArray = document.getElementsByTagName("a");
    for(j = 0; j < imgArray.length; j++) {
      if(imgArray[j].className.length > 0) {
        imgArray[j].style.display = (imgArray[j].className == cat) ? "inline" : "none";
      }
    }
  }
  
  // incorrect parameter
  else {
    alert("'" + cat + "' is not a valid category");
  }
}