How to use vuex namespaced getters with arguments?

You can also declare a getter function like this:

feedersById: (state) => rowID => {
  if (state.feedersArray.hasOwnProperty(rowId)) {
    return state.feedersArray[rowId].map(id => state.feeders[id]);
  }
}

feedersById(state) {
    return rowId => {
        if (state.feedersArray.hasOwnProperty(rowId)) {
            return state.feedersArray[rowId].map(id => state.feeders[id]);
        }

    }
},

feedersId() {
  if (this.rowData) {
   return this.$store.getters['feeders/feedersById'](this.rowData.ac_id);
  }
}

Okey I had some mistake there and now it works properly. Thanks!! :)