ruby将两个语句合并为一个

Question

This question is for very very specific case, where I may change params. This is not a part of any rails app.

params is {:email => " ab", :xyz => " ", :opq => nil} I run following :

params.each{|_, v| v.strip! if v}
params.keep_if{|_, v| v.length > 0 if v}

to get params as {:email => "ab"}

is there anyway to merge above two lines into one?

Answer 1

ruby-1.9.3-p125 :011 > params ={:email => " ab", :xyz => " ", :opq => nil}
 => {:email=>" ab", :xyz=>" ", :opq=>nil} 
ruby-1.9.3-p125 :012 > params.reject! { |_, v| !v || v.strip!.length == 0 }
 => {:email=>"ab"}

Answer 2

params.each{|_, v| v.strip! if v}.reject!{|_, v| !v || v.length == 0}

Answer 3

Actually, the lines you wrote are chainable:

params.each{|_, v| v.strip! if v}.keep_if{|_, v| v.length > 0 if v}

This works because each returns the object itself (which was updated). However, IMHO in-place updates are usually a bad idea, so here's a functional approach:

params2 = Hash[params.map { |k, v| [k, v.strip] if v && v.strip.size > 0 }.compact]

But this is unnecessarily verbose because the stdlib lacks some fundamental abstractions. With the aid of Enumerable#mash and Object#present? it's as simple as:

params2 = params.mash { |k, v| [k, v.strip] if v.present? }

Answer 4

Here is one option that seems to technically answer your question, but I'm guessing it is not what you are looking for:

params.select{|_,v| v.strip.length > 0 if v}

The fundamental trouble you are running into is that Hash#map does not return a Hash but rather an Array. Many people, including myself, find this annoying. See for example: http://www.ruby-forum.com/topic/185611

Here is a verbose option using inject.

params.inject({}) {|h,(k,v)| h.merge(k => v ? v.strip : v)}.select{|_,v| v.length > 0 if v}

If it matters to you, neither of these solutions will make any destructive changes to params.

1.9.3-p125 :030 > params = {:email => " ab", :xyz => " ", :opq => nil}
 => {:email=>" ab", :xyz=>" ", :opq=>nil} 
1.9.3-p125 :031 > params.inject({}) {|h,(k,v)| h.merge(k => v ? v.strip : v)}.select{|_,v|   v.length > 0 if v}
 => {:email=>"ab"} 
1.9.3-p125 :032 > params
 => {:email=>" ab", :xyz=>" ", :opq=>nil} 

Inject is a tricky function that takes some getting used to. I'll try to explain this line step by step:

• params.inject({}} says to create an empty hash to store our results in.
• |h, (k,v)| says to pass the new empty hash into the variable h while also passing the key, value pair from our original params hash into k, v respectively.

Next it get's kindof hairy. I'll unpack the next command from the inside out.

• v ? v.strip : v v ? v.strip : v uses the ternary operator to return v.strip in the case that v evaluates to true or v in the case that v is false or nil

• k => v ? v.strip : v k => v ? v.strip : v creates a new hash with the result

• h.merge(k => v ? v.strip : v) merges our new hash into h, which started out empty, and then passes the result onto the next iteration of the inject loop.

• in the next iteration of the loop, h will no longer be empty and future results will continue to be merged onto it.

At this point we have stripped the hash and if we stopped here the result looks like this:

1.9.3-p125 :032 > params
 => {:email=>" ab", :xyz=>" ", :opq=>nil} 
1.9.3-p125 :033 > params.inject({}) {|h,(k,v)| h.merge(k => v ? v.strip : v)}
 => {:email=>"ab", :xyz=>"", :opq=>nil} 

Now that the hash is stripped, the select statement is straight forward. I use select here rather than keep_if, because, despite the lack of a !, keep_if is a destructive method. See this rant: http://news.ycombinator.com/item?id=2247352 . Since our inject statement returns a hash we can directly call .select on it, although I don't suggest making your lines of code this long in actual practice.

1.9.3-p125 :034 > params
 => {:email=>" ab", :xyz=>" ", :opq=>nil} 
1.9.3-p125 :035 > params.inject({}) {|h,(k,v)| h.merge(k => v ? v.strip : v)}.select{|_,v| v.length > 0 if v}
 => {:email=>"ab"} 

Answer 5

params.keys.each{|k| v = h.delete(k); h[k] = v.strip if v and !v.empty?}

要么

params.select!{|k, v| v and v.strip!; v and !v.empty?}