text: import React from 'react';
  import { connect } from 'react-redux';
  import Header from './Header';
  import getVariables from '../selectors/getVariables';
  
  const mapStateToProps = (state) => {
    return {
      columnNames: getVariables(state.expression)
    };
  };
  
  export default connect(mapStateToProps, null)(Header);
  