Combine data and find duplicates based on a search value

I have an object as follows:

const overall = {
    mainData: {
        id: 1,
        group: 'grp0'
    },
    data: [
        {
            id: 2,
            group: 'grp3'
        },
        {
            id: 3,
            group: 'grp3'
        }
    ]
}

I want to do a combined check across both mainData and data.

Search for a particular grp in a them. For example searching for grp3.

If there is at least 2 grp3, return true, else return false.

In the above, result will be true cos there is 2 grp 3.

Another example where it will be true. two grp3.

const overall = {
    mainData: {
        id: 1,
        group: 'grp3'
    },
    data: [
        {
            id: 2,
            group: 'grp3'
        }
    ]
}

An example where it will be false. Only 1 grp3

const overall = {
    mainData: {
        id: 1,
        group: 'grp0'
    },
    data: [
        {
            id: 1,
            group: 'grp1'
        },
        {
            id: 2,
            group: 'grp2'
        },
        {
            id: 3,
            group: 'grp3'
        },
        {
            id: 4,
            group: 'grp4'
        }
    ]
}

How could I achieve this in a single flow of filters and maps?

Currently performing this which feels verbose.

const mainGroup = [overall.mainData];
const dataGroups = overall.data.filter(d => d.group);
const allGroups = [...mainGroup, ...dataGroups];
const isMorethanOneItem = allGroups.filter(item => item.group === 'grp3').length > 1;

>Solution :

Basedon your code, we can reduce it to one line

let contains = [overall.mainData,...overall.data].filter(d => d.group == key).length > 1

const overall = {
    mainData: {
        id: 1,
        group: 'grp0'
    },
    data: [
        {
            id: 2,
            group: 'grp3'
        },
        {
            id: 3,
            group: 'grp3'
        }
    ]
}

let key ='grp3'
let result = [overall.mainData,...overall.data].filter(d => d.group == key).length > 1
console.log(result)