How to filter array based on selected item

Question

I have an array of objects in an json file:

[
  {
    "department": "Sound Department",
    "subDepartments": [
      "Supervising Sound Editor",
      "Dialog Editor",
      "Sound Designer",
      "Foley Artis",
      "Sound Recordist"
    ]
  },
  {
    "department": "Camera Department",
    "subDepartments": [
      "Camera Operator",
      "Second Assistant Camera",
      "Other Assistant Camera",
      "Steadycam Operator",
      "Focus Puller"
    ]
  },
  {
    "department": "Production Department",
    "subDepartments": [
      "Camera Operator",
      "Second Assistant Camera",
      "Other Assistant Camera",
      "Steadycam Operator",
      "Focus Puller"
    ]
  }
]

From this i'm creating a dropdown menu of Departments. From that i would like to create another dropdown menu of sub-departments based on which department have been selected.

The dropdown menu of Departments is working fine, as well as storing that department in a state. I just can't figure out how to filter these.

import React, { useState } from "react";
import "./CreateJobPage3.css"

import Button from "../Input/Button";
import Select from "../Input/Select";
import departmentData from "../Data/departmentSheet.json";

const CreateJobPage3 = (props) => {
    const [department, setDepartment] = useState()
    const [subDepartment, setSubDepartment] = useState()

    const departments = departmentData.map((data) => data.department)

    const subDepartments = departmentData.filter(item => {
        return item.department === department;
      });

    const departmentHandler = (props) =>{
        setDepartment(props)
    }

    const subDepartmentHandler = (props) =>{
        setSubDepartment(props)
    }

  return (
    <>
      <div className="CJP3___inner">
          <Select
            placeholder="Choose Department"
            options={departments}
            value={department}
            onChangeOption={departmentHandler}
          />
          <Select
            placeholder="Choose Department"
            options={subDepartments}
            value={subDepartment}
            onChangeOption={subDepartmentHandler}
            isMulti={true}
          />
      </div>
      <Button className="isGrey formButton" text={"Add Function"} />
    </>
  );
};

export default CreateJobPage3;

Answer 1

So you already have filtering, what you are missing is getting subDepartments property out of the object, for that you could use map , but because your subDepartments is itself an array, I would use flatMap , otherwise result would be [['sub1,'sub2']]

      const subDepartments = departmentData.filter(item => {
        return item.department === department;
      }).flatMap(item => item.subDepartments);

Answer 2

2 issues here. By using Array.filter your result is going to be an array of the whole department object, whereas you just want the subdepartments. In this case, it's a little quicker to use Array.find and then just access the subDepartments array.

 const departmentData = [{ "department": "Sound Department", "subDepartments": [ "Supervising Sound Editor", "Dialog Editor", "Sound Designer", "Foley Artis", "Sound Recordist" ] }, { "department": "Camera Department", "subDepartments": [ "Camera Operator", "Second Assistant Camera", "Other Assistant Camera", "Steadycam Operator", "Focus Puller" ] }, { "department": "Production Department", "subDepartments": [ "Camera Operator", "Second Assistant Camera", "Other Assistant Camera", "Steadycam Operator", "Focus Puller" ] } ] let department = "Production Department" const subDepartments = departmentData.filter(item => { return item.department === department; }); console.log('Current Method:', subDepartments) const subDepartmentsNew = departmentData.find(item => { return item.department === department; }).subDepartments; console.log('New Method:', subDepartmentsNew)