How to enumerate interface keys to make new interface that the value is depend on the key

How to iterate interface keys to make new interface that the value is depend on the key.

type IParse<T> = {
	[K in keyof T as K extends string ? K : never]: string // How to make if K === 'a' the type should be number
}

interface X {
	a: number
	b: string
	c: string[]
	d: number[]
}

type Result = IParse<X>

// Actual result

interface Actual {
    a: string
    b: string
    c: string
    d: string
}

// Expected result

interface Expected {
    a: number
    b: string
    c: string
    d: string
}

Playground

You can do it by adding a conditional to the value portion of what you have:

type IParse<T> = {
	[K in keyof T as K extends string ? K : never]: 
        K extends "a" ? number : string; // <======================
};

interface X {
	a: number;
	b: string;
	c: string[];
	d: number[];
}

type Result = IParse<X>;
//   ^? -- type Result = {a: number; b: string; c: string; d: string; }

Playground link