Delete multiple hash keys

Question

I often find myself writing this:

params.delete(:controller)  
params.delete(:action)  
params.delete(:other_key)  
redirect_to my_path(params)

The trail of deletes doesn't feel right and neither does:

[:controller, :action, :other_key].each do |k|
  params.delete(k)
end

Is there anything simpler and cleaner?

When I wrote that the second approach didn't feel right, I meant that given the richness of the Hash API, I suspected that there was some method or idiom already out there for this and a monkey patch wouldn't be necessary. Maybe not, though. Many thanks to all who answered! — Mark Westling
– Mark Westling, Commented Oct 13, 2009 at 15:08
Hash#except was exactly what I was looking for. I didn't remember that it's a Rails core extension so I was puzzled when I couldn't find it in the Hash API. — Mark Westling
– Mark Westling, Commented Oct 13, 2009 at 16:15
Note that strictly the answer is Hash#except! but Hash#except is the way to go (don't mess with params!). As a rule of thumb, don't mess with any object in-place unless absolutely required, the side-effects may be have unexpected results. — tokland
– tokland, Commented Aug 19, 2013 at 11:36

Dominic Sayers · Accepted Answer · 2014-05-22 14:51:17Z

239

I'm guessing you're unaware of the Hash#except method ActiveSupport adds to Hash.

It would allow your code to be simplified to:

redirect_to my_path(params.except(:controller, :action, :other_key))

Also, you wouldn't have to monkey patch, since the Rails team did it for you!

edited May 22, 2014 at 14:51

Dominic Sayers

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answered Oct 13, 2009 at 15:43

Ben Crouse

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5 Comments

Mark Westling Over a year ago

Ahhh, I knew I'd seen this before but I couldn't remember where! (Hence my "this doesn't feel right" remark.) Thanks!

tadman Over a year ago

One of those lesser documented methods. I went looking for something like this while proposing an answer but didn't see it.

Trip Over a year ago

For some reason except didn't work. But except! did. Rails 3.0

house9 Over a year ago

Rails 3.2 on ActiveRecord attributes, had to use strings for the keys? i.e. User.attributes.except("id", "created_at", "updated_at") symbols did not work

FireDragon Over a year ago

Adding to what @house9 mentioned, ActiveRecord attributes method returns a Hash with keys that are String. So then you would have to use string key names in .except(). However I get around this using the Hash.symbolize_keys a la @user.attributes.symbolize_keys.except(:password, :notes) -- using symbolize_keys makes it work as one would expect

Fralcon · Accepted Answer · 2020-10-16 00:03:43Z

46

While using Hash#except handles your problem, be aware that it introduces potential security issues. A good rule of thumb for handling any data from visitors is to use a whitelist approach. In this case, using Hash#slice instead.

params.slice!(:param_to_keep_1, :param_to_keep_2)
redirect_to my_path(params)

edited Oct 16, 2020 at 0:03

Fralcon

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answered Oct 14, 2009 at 19:57

user190125

4 Comments

David J. Over a year ago

Thanks for mentioning the security issues surrounding redirection.

David J. Over a year ago

Just a heads up: ActiveSupport, not Ruby itself, provides Hash#slice and #slice! as.rubyonrails.org/classes/ActiveSupport/CoreExtensions/Hash/…

Dominic Sayers Over a year ago

I couldn't get David James's link to work but this one seems to be ok: api.rubyonrails.org/classes/Hash.html#method-i-slice

Khurram Raza Over a year ago

undefined method 'slice!' for {:b=>2, :c=>3}:Hash

Bob Aman · Accepted Answer · 2009-10-13 15:32:28Z

28

I'd be completely happy with the code you originally posted in your question.

[:controller, :action, :other_key].each { |k| params.delete(k) }

answered Oct 13, 2009 at 15:32

Bob Aman

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2 Comments

Dan Bradbury Over a year ago

without modifying Hash this is the best answer :+1:

Pablo Over a year ago

I've used this method but replaced params with the name of the hash and then it worked!! The hash gets mutated.

Mike Seplowitz · Accepted Answer · 2013-07-29 16:23:42Z

15

Another way to phrase dmathieu's answer might be

params.delete_if { |k,v| [:controller, :action, :other_key].include? k }

edited Jul 29, 2013 at 16:23

answered Oct 13, 2009 at 14:38

Mike Seplowitz

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Comments

the_spectator · Accepted Answer · 2021-08-17 19:39:44Z

10

Starting from Ruby 3.0, Hash#except is supported directly. This means we would not need activesupport to access Hash#except.

From documentation:

Hash#except(*keys) → hash

This method returns a new hash, which includes everything from the original hash except the given keys.

example:

h = { a: 100, b: 200, c: 300, d: 400 }
h.except(:a, :d) #=> {:b=>200, :c=>300}

Reference:

https://docs.ruby-lang.org/en/3.0.0/Hash.html#method-i-except

answered Aug 17, 2021 at 19:39

the_spectator

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Comments

MrYoshiji · Accepted Answer · 2014-02-18 21:14:10Z

7

Fire up a monkey patch?

class Hash
  def delete_keys!(*keys)
    keys.flatten.each do |k|
      delete(k)
    end

    self
  end

  def delete_keys(*keys)
    _dup = dup
    keys.flatten.each do |k|
      _dup.delete(k)
    end

    _dup
  end
end

edited Feb 18, 2014 at 21:14

MrYoshiji

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answered Oct 13, 2009 at 14:31

tadman

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5 Comments

Bob Aman Over a year ago

Monkey patches are a tool of last resort.

David Seiler Over a year ago

Monkey patches that replace existing functions are a tool of last resort. Monkey patches that add new functions are Ruby 101.

Vincent Over a year ago

Should be delete(k) instead of delete(key)

Phrogz Over a year ago

For code maintenance the implementation of the non-destructive delete_keys should be simply dup.delete_keys!(*keys)

tadman Over a year ago

@Phrogz Defining one in terms of the other isn't always a bad idea, but it's just left here unrolled for clarity.

Community · Accepted Answer · 2017-05-23 10:31:19Z

2

I don't know what you think is wrong with your proposed solution. I suppose you want a delete_all method on Hash or something? If so, tadman's answer provides the solution. But frankly, for a one-off, I think your solution is extremely easy to follow. If you're using this frequently, you might want to wrap it up in a helper method.

edited May 23, 2017 at 10:31

CommunityBot

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answered Oct 13, 2009 at 14:35

Pesto

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