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## Declaratively Map Predicates to Object Properties Using Ramda where

#### Declaratively Map Predicates to Object Properties Using Ramda where

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Sometimes you need to filter an array of objects or perform other conditional logic based on a combination of factors. Ramda's `where` function gives you a concise way to declaratively map individual predicates to object properties, that when combined, cover the various facets of your conditions. In this lesson, we'll look at how this powerful function can be used for scenarios requiring a complex predicate function.
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Sometimes you need to filter an array of objects or perform other conditional logic based on a combination of factors. Ramda's `where` function gives you a concise way to declaratively map individual predicates to object properties, that when combined, cover the various facets of your conditions. In this lesson, we'll look at how this powerful function can be used for scenarios requiring a complex predicate function.

Hozefa

Whats the advantage of using `Ramda` over `lodash`? They look to doing very similar things.

I'll start by saying that `lodash` is an awesome library, I have nothing against it. That being said, the biggest advantage `Ramda` has over `lodash` is the combination of argument order and automatic function currying. So, for something like `filter`, `lodash` takes the collection as the first argument, where `ramda` takes the predicate function first, and it then curries that function. So, `R.filter(x => x % 2 == 0)` returns a new function that you just have to pass data to. To accomplish the same thing with `lodash`, it would look like this: `_.partial(_.filter, _, (x) => x%2==0)` where you need to use partial application to return a partially applied version of `filter` function and a placeholder to account for the fact that I don't have the data yet and it is expected as the first argument to filter.
You can accomplish the same things with the functional programming variant of `lodash`, `lodash/fp`. Using `lodash/fp` gets you most of the same capabilities, but it doesn't offer lenses, and lenses can be very powerful.