Describing what I want to do is fairly simple. I want to use this command but in code:

/data modify entity @e[type=minecraft:zombie,sort=nearest,limit=1] HandDropChances set value [0.0f, 0.0f]

The entity and the fact that it contains HandDropChances are already known, so ignore those parts of the issue

the specific part I am struggling with is making it accept [0.0f, 0.0f]

the following is part Java and part psuedocode of what I am looking to do.

void someVoid(Entity ent) {
  CompoundTag compTag = ent.saveWithoutId(new CompoundTag());
  String name = "HandDropChances";
  if (compTag.contains(name)) {
    //.setTag doesn't exist of course,
    //and [0.0f, 0.0f] is nonsense,
    //but I don't know how I ought to declare it in order to get it into the form I need to actually achieve this.
    compTag.setTag(name, [0.0f, 0.0f]);
    
    // What I've been trying to do to make this happen is below
    ListTag tagList = (ListTag) compTag.get(name);
    tagList.clear();
    tagList.add(0.0f);
    tagList.add(0.0f);
    compTag.remove(name);
    compTag.put(tagList);
    //or something like that, anyway. but floats aren't Tags so this, of course, doesn't work
  }
}

 

There's a TagParser class if you want to explore what gets created for some SNBT.

But I think what you are looking for is FloatTag?

 

Thanks! I think I'd been in such a headache over it all day that I just missed the fact that I'd already found that part of the answer, your stating the obvious is what finally pushed me up onto the ledge. I appreciate it.

Why are you doing this so complicated?

you can simply call Mob#setDropChance with EquipmentSlot#MAINHAND and EquipmentSlot#OFFHAND and the value you want,
if you wish a guaranteed drop you can also call Mob#setGuaranteedDrop