Ramda如果两者都匹配，则省略键和值

Question

I have an object that contains some data. I'd like to pick out certain keys and then also omit a key and value if they both match. Here's my object:

const obj = {
  title: 'some title',
  description: 'some descrption',
  image: 'default_image.png'
}

What I'd like to do, is to extract description and image , and then omit the image if it has a value of 'default_image.png' .

const fn = R.compose(
  // if image === 'default_image.png' then omit it
  R.pickAll(['description', 'image'])
)

Not sure what the best ramda function is to use for the second part of the above.

Answer 1

You could create two different functions and one boolean function that checks for the field applying it with ramda's ifElse

const obj1 = {
  title: 'some title',
  description: 'some descrption',
  image: 'default_image.png'
}

const obj2 = {
  title: 'title',
  description: 'descrption',
  image: 'image.png'
}

const withImage = R.pickAll(['description', 'image']);
const withoutImage = R.pickAll(['description']);
const hasDefault = obj => obj['image'] == 'default_image.png'

const omit = R.ifElse(hasDefault, withoutImage, withImage);

console.log(omit(obj1));
console.log(omit(obj2));

The simplest way I could think of is using pickBy

const hasDefault = (val, key) => key == 'image' && val == 'default_image.png' ? false : true
console.log(R.pickBy(hasDefault, obj1))
console.log(R.pickBy(hasDefault, obj2))

Answer 2

I would probably do something like

const fn = pipe(
  when(propEq('image', 'default_image.png'), dissoc('image')),
  pick(['description', 'image'])
);

dissoc returns a copy of an object with a specific key removed. propEq tests if the given property of an object matches the value supplied. And when takes a predicate and a conversion function. If the predicate matches the supplied data, the result of calling the conversion function on that data is returned, otherwise that data is returned unchanged.

Note that I chose pick instead of pickAll . The only difference is that pick skips keys it doesn't find, pickAll returns them with value undefined .

You can see this in the Ramda REPL .

If you were always going to operate on a list instead of individual objects, you might switch from pick to project :

const fn = pipe(
  project(['description', 'image']),
  map(when(propEq('image', 'default_image.png'), dissoc('image')))
);

fn(objects);

This one is also available on the Ramda REPL .