wordpress get_category_by_slug if true add add class

Question

Good afternoon , this is the problem : I have an asside menu , this menu has 4 categories and each of this categories has many subcategories , What I am trying to do is that when I am on the page of a subcategory I give a class to a

on the left menu , a class of active so the category of the subcategory I am in stays opens . Whole code here : https://pastebin.com/Q09eE9nB

$categories = get_categories( array(
'orderby' => 'name',
'order'   => 'ASC',
'parent' => 52,
'hide_empty' => 0

));

            <?php if( $categories ): ?>
        <ul class="main-categ">
            <?php foreach ( $categories as $kCat => $vCat ): ?>
                <li class="main-item <?php echo get_category_by_slug( $categories ) == $subCategories ? 'active' : ''; ?>"><?php
                                $subCategories = get_categories( array(
                                    'orderby' => 'name',
                                    'order'   => 'ASC',
                                    'parent' => $vCat->cat_ID,
                                    'hide_empty' => 0
                                ));?>

                <a class="main-link" href="#<?php echo $vCat->slug; ?>" data-cat="<?php echo $vCat->slug; ?>"><?php echo $vCat->name; ?></a>
                <?php if( $subCategories ): ?>
                <ul class="subcateg">
                    <?php foreach ( $subCategories as $kSub => $vSub ): ?>
                    <li><a href="<?php echo esc_url( get_category_link( $vSub->cat_ID ) ); ?>"><i class="fa fa-angle-double-right"></i> <?php echo $vSub->name; ?></a></li>
                    <?php endforeach; ?>
                </ul>
                <?php endif; ?>
            </li>
            <?php endforeach; ?>
        </ul>

Answer 1

Solution :

$thisCat = get_category( get_query_var( 'cat' ) );


            <ul class="main-categ">
            <?php foreach ( $categories as $kCat => $vCat ): ?>
                <li class="main-item <?php echo $thisCat->category_parent == $vCat->cat_ID ? 'active' : ''; ?>"><?php
                                $subCategories = get_categories( array(
                                    'orderby' => 'name',
                                    'order'   => 'ASC',
                                    'parent' => $vCat->cat_ID,
                                    'hide_empty' => 0
                                ));?>

                <a class="main-link" href="#<?php echo $vCat->slug; ?>" data-cat="<?php echo $vCat->slug; ?>"><?php echo $vCat->name; ?></a>
                <?php if( $subCategories ): ?>
                <ul class="subcateg">
                    <?php foreach ( $subCategories as $kSub => $vSub ): ?>
                    <li class="<?php echo get_query_var( 'cat' ) == $vSub->cat_ID ? 'activ':'';?>"><a href="<?php echo esc_url( get_category_link( $vSub->cat_ID ) ); ?>"><i class="fa fa-angle-double-right"></i> <?php echo $vSub->name; ?></a></li>
                    <?php endforeach; ?>
                </ul>
                <?php endif; ?>
            </li>
            <?php endforeach; ?>
        </ul>