How to set state within a reducer

I have an array of product objects inside my reducer and I have an empty array of brand as well. I want to add all the unique brands from my products object array into my brands array in my reducer, is there any way I can do that?

My Reducer:

import * as actionTypes from './shop-types';

 const INITIAL_STATE = {
 products: [
{
  id: 1,
  brand:"DNMX"
},
{
  id: 2,
  brand: "Aeropostale",
},
{
  id: 3,
  brand: "AJIO",
},
{
  id: 4,
  brand: "Nike",
},
],
  cart: [],
  brands: [], //<---- I want to add all the unique brands inside this array
  currentProduct: null,
};

  const shopReducer = (state = INITIAL_STATE, action) => {
  switch (action.type) {
  case actionTypes.ADD_TO_CART:
  const product = state.products.find(
    (product) => product.id === action.payload.id
  );
  if (product !== null) {
    return {
      ...state,
      cart: state.cart.concat(product),
    };
  } else {
    return null;
  }
default:
  return state;
 }
 };

export default shopReducer;