public inherited sharing class dataTableController {
    
    @AuraEnabled(Cacheable = true)
    public static List<ActivityHistory> getActivity(string leadId, string contactId){
        List<Lead> leadQueryList;
        List<Contact> ctactQueryList;  
        List<ActivityHistory> activityList = new List<ActivityHistory>(); //variable to hold the list of activitiyhistories
        
        leadQueryList = [                           //query all activity history related to the lead (return list of leads w nested ah lists)
                        SELECT 	Id,
                                (SELECT
                                    Id, 
                                 	Subject, 
                                 	ActivityDate, 
                                 	OwnerId,
                                    Activity_Type__c                                                                 	                                 	                            
                                 FROM ActivityHistories)
                        FROM Lead
                        WHERE Id = :leadId];

        ctactQueryList = [                           //query all activity history related to the ctact (return list of ctact w nested ah lists)
                        SELECT 	Id,
                                (SELECT
                                    Id, 
                                 	Subject, 
                                 	ActivityDate, 
                                 	OwnerId,
                                    Activity_Type__c                                                                 	                                 	                            
                                 FROM ActivityHistories)
                        FROM Contact
                        WHERE Id = :contactId];

        for (Lead ld : leadQueryList) {               //loop through lead list
            if(!ld.ActivityHistories.isEmpty()){
                for (ActivityHistory h: ld.ActivityHistories){
                    activityList.add(h);
                }
            }
        }

        for (Contact c : ctactQueryList) {               //loop through ctact list
            if(!c.ActivityHistories.isEmpty()){
                for (ActivityHistory h: c.ActivityHistories){
                    activityList.add(h);
                }
            }
        }
        return activityList;
    }
}

import {LightningElement, wire, track, api} from 'lwc';
import { getRecord, getFieldValue } from 'lightning/uiRecordApi';

import CONTACTID_FIELD from '@salesforce/schema/Lead.contactId__c';

// importing apex class methods
import getActivity from '@salesforce/apex/dataTableController.getActivity';

// datatable columns with row actions
const columns = [
    {
        label: 'Date',
        fieldName: 'ActivityDate',
        sortable: "true"
    }, {
        label: 'Activity Type',
        fieldName: 'Activity_Type__c',
        sortable: "true"
    }, {
        label: 'Subject',
        fieldName: 'Subject',
        sortable: "true"
    }, {
        label: 'Assigned',
        fieldName: 'OwnerId',
        sortable: "true"
    },
];

export default class DataTableWithSortingInLWC extends LightningElement { 
    // reactive variable
    @track data;
    @track columns = columns;
    @track sortBy;
    @track sortDirection;
    @api recordId;

    // retrieving the data using wire service
    @wire(getRecord,{recordId: '$recordId' , fields: CONTACTID_FIELD})
    lead;

    @wire(getActivity, {leadId: '$recordId', contactId: lead.CONTACTID_FIELD })

    
    activities(result) {
        if (result.data) {
            this.data = result.data;
            this.error = undefined;

        } else if (result.error) {
            this.error = result.error;
            this.data = undefined;
        }
    }

    handleSortdata(event) {
        // field name
        this.sortBy = event.detail.fieldName;

        // sort direction
        this.sortDirection = event.detail.sortDirection;

        // calling sortdata function to sort the data based on direction and selected field
        this.sortData(event.detail.fieldName, event.detail.sortDirection);
    }

    sortData(fieldname, direction) {
        // serialize the data before calling sort function
        let parseData = JSON.parse(JSON.stringify(this.data));

        // Return the value stored in the field
        let keyValue = (a) => {
            return a[fieldname];
        };

        // cheking reverse direction 
        let isReverse = direction === 'asc' ? 1: -1;

        // sorting data 
        parseData.sort((x, y) => {
            x = keyValue(x) ? keyValue(x) : ''; // handling null values
            y = keyValue(y) ? keyValue(y) : '';

            // sorting values based on direction
            return isReverse * ((x > y) - (y > x));
        });

        // set the sorted data to data table data
        this.data = parseData;

    }
}

<template>
    <lightning-card title="Sorting Data in Lightning Datatable in LWC" icon-name="standard:lead" > <br/>
        <div style="width: auto;">
            <template if:true={data}>
                <lightning-datatable data={data}
                                     columns={columns}
                                     key-field="id"
                                     sorted-by={sortBy}
                                     sorted-direction={sortDirection}
                                     onsort={handleSortdata}
                                     hide-checkbox-column="true"></lightning-datatable>
            </template>

        </div>
    </lightning-card>
</template>