map a prefix on array of hashes and set a parameter in a promise chain

Question

// I want to map a prefix ("myPrefix") to each member of the array and use it later like this "myPrefix:yshepu" inside the Redis.prototype.exists function. This is, because in the Redis DB I have different prefix:hash types.

The "exists" function return 0 or 1 and the "getActive" function should later return a filtered result array where only the pure hashes stay in the array. The Filter eleminates the not existing array items. The result array items should not have the prefix "myPrefix". Only for the Redis lookup the prefix should temporally be used for lookup the correct hash. I hope there is a solution, so that I don't need to use array.map 3 times

• map prefix to each array item
• compute the whole map again to eleminate the prefix from each array item again

Is there an elegant and performant way to do this in the context?

This is the code:

var array = ["yshepu","mmxhhb", "qwertz", "wvlgrs", "knfght"];  
var prefix = "myPrefix";

Redis.prototype.getActive = function (prefix, array) {
    var self = this;

    return this.Q.all(array.map(self.exists.bind(self)))
        .then(function (res) {
            return array.filter(function (val, idx) {
                return res[idx];
            });
        });
};


Redis.prototype.exists = function (prefix, key) {

    return this.client.exists(prefix + ':' + key)
        .then(function (data) {

            return data; /* res is 0 or 1 */
        });
};