How can a radio button change an <option> of a drop-down list in JS?

Question

my goal is for radio buttons to change an <option> of a <select> element (drop-down list).

I was already able to solve the reverse behavior (selecting another <option> results in a change in a radio button). As you can see here:

function validate()
{
 var x = document.getElementById("location_select");
 var y = x.options[x.selectedIndex].value;
   {
    document.getElementById(y).checked = true;
   }
}

<select id="location_select" onchange="validate()">
  <option value="berlin">Berlin</option>
  <option value="paris">Paris</option>
</select>

<label>
  <input type="radio" id="berlin" name="location">
  <span>Berlin</span>
</label>

<label>
  <input type="radio" id="paris" name="location">
  <span>Paris</span>
</label>

Now I would like to generate the reverse behavior. Desired Behavior: Changing the radio button also changes the <option> in my selection.

The radio button ID is the same as the "value" of my drop-down options. So a JS variable can then be used for the ID as well as the "value".

Basically, this is my progress currently:

function validate_2()
{
   {
     document.getElementById("location_select").selectedIndex = "1";
   }
}

<label>
  <input type="radio" id="berlin" name="location" onchange="validate_2()">
  <span class="title">Berlin</span>
</label>

<label>
  <input type="radio" id="paris" name="location" onchange="validate_2()">
  <span class="title">Paris</span>
</label>

<select id="location_select">
  <option value="berlin">Berlin</option>
  <option value="paris">Paris</option>
</select>

As you can see, it's only static so far.
I'm open to better methods if this isn't a good one.

Answer 1

This function can change selected option of <select> by changing radio inputs

Get the id of the radio input which was changed and set value attribute of <select> tag

Version 1

function validate_2() {
    checkedVal = event.target.id;
    locationSelect = document.getElementById("location_select");
        
    locationSelect.value = checkedVal;
}

Version 2

It can be shortened to

function validate_2() {
    // ID becomes variable in JS
    location_select.value = event.target.id;
}

Version 3

Using selectedIndex explicitly

function validate_2() {
    checkedVal = event.target.id;
    locationSelect = document.getElementById("location_select"); 
    indexToSelect = Array.from(locationSelect.options).findIndex(opt => opt.value == checkedVal);
    locationSelect.selectedIndex = indexToSelect;
}

Answer 2

function validate_2(city)
{
   
     document.getElementById("location_select").value = city;
   
}

function validate_1(){
  

    radio = document.getElementsByTagName('input')
    
    if(radio[0].checked)radio[1].checked = true
    else if (radio[1].checked)radio[0].checked = true
    


}

<label>
  <input type="radio" id="berlin" name="location" onchange="validate_2('berlin')" checked>
  <span class="title">Berlin</span>
</label>

<label>
  <input type="radio" id="paris" name="location" onchange="validate_2('paris')">
  <span class="title">Paris</span>
</label>

<select id="location_select" onChange="validate_1()">
  <option value="berlin">Berlin</option>
  <option value="paris">Paris</option>
</select>