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IMHO this question is too abstract to be of any transferrable value - you haven't said why you want to do this, though I suspect your example is simply too generic.

I'm not saying there isn't any value in such a reduction algorithm; it's just meaningless without context – anyone who answers has no guarantee they'll be providing something of practical use.

• Where is the data coming from?
• What value should be in the final nested result?
• Will the structure already exist?
• Can it take an input value?
• Will it done by machines or humans?
• Etc...

If all these are requirements, I suggest looking at Lodash set() :

• https://lodash.com/docs/4.17.4#set

Sets the value at path of object. If a portion of path doesn't exist, it's created. Arrays are created for missing index properties while objects are created for all other missing properties. Use _.setWith to customize path creation.

As a programming exercise, my take on it is:

function set(keys, value, obj) {
    obj = obj || {}
    keys = typeof keys === 'string'
        ? keys.match(/\w+/g)
        : Array.prototype.slice.apply(keys)
    keys.reduce(function(obj, key, index) {
        obj[key] = index === keys.length - 1 
            ? value 
            : typeof obj[key] === 'object' && obj !== null
                ? obj[key]
                : {}
        return obj[key]
    }, obj)
    return obj
}

// new object
var obj = set(['a', 'b', 'c'], 1)
//  { a: { b: { c: 1 } } } 

// existing objects
set(['b', 'c'], 2, obj)
// { a: { b: { c: 1 } }, b: { c: 2 } } 

// new props
set(['x', 'y'], 3, obj.b)
// { a: { b: { c: 1 } }, b: { c: 2, x: { y: 3 } } } 

// existing props
set(['x', 'z'], 4, obj.b)
// { a: { b: { c: 1 } }, b: { c: 2, x: { y: 3, z: 4 } } } 

// keys as string
set('x y z', 5, obj)
// { a: { b: { c: 1 } }, b: { c: 2, x: { y: 3, z: 4 } }, x: { y: { z: 5 } } }

obj

In general programming terms, usability and practicality is more valuable than brevity or speed.