Ruby Arrays: Select(), Collect(), and Map()
The Syntax for Mapping: a = ["A", "B", "C", "D"] #=> ["A", "B", "C", "D"] A. Map {|Item|"A" == Item} #=> [True, False, False, False] A. Select {|Item|"A" ==...
The syntax for mapping:
a = ["a", "b", "c", "d"] #=> ["a", "b", "c", "d"]
a.map {|item|"a" == item} #=> [true, false, false, false]
a.select {|item|"a" == item} #=> ["a"]
Question how about if I have:
irb(main):105:0> details[1]
=> {:sku=>"507772-B21", :desc=>"HP 1TB 3G SATA 7.2K RPM LFF (3 .", :qty=>"",
:qty2=>"1", :price=>"5,204.34 P"}
I want to delete every entry which has an empty qty value on this array or select only the ones with some value in it.
I tried:
details.map {|item|"" == item}
Just returns a lot of false and then when I use the same just change map to select I get:
[]
3 Answers
It looks like details is an array of hashes. So item inside of your block will be the whole hash. Therefore, to check the :qty key, you'd do something like the following:
details.select{ |item| item[:qty] != "" }
That will give you all items where the :qty key isn't an empty string.
EDIT: I just realized you want to filter details, which is an array of hashes. In that case you could do
details.reject { |item| item[:qty].empty? }
The inner data structure itself is not an Array, but a Hash. You can also use select here, but the block is given the key and value in this case:
irb(main):001:0> h = {:sku=>"507772-B21", :desc=>"HP 1TB 3G SATA 7.2K RPM LFF (3 .", :qty=>"", :qty2=>"1", :price=>"5,204.34 P"}
irb(main):002:0> h.select { |key, value| !value.empty? }
=> {:sku=>"507772-B21", :desc=>"HP 1TB 3G SATA 7.2K RPM LFF (3 .",
:qty2=>"1", :price=>"5,204.34 P"}
Or using reject, which is the inverse of select (excludes all items for which the given condition holds):
h.reject { |key, value| value.empty? }
Note that this is Ruby 1.9. If you have to maintain compatibility with 1.8, you could do:
Hash[h.reject { |key, value| value.empty? }]
When dealing with a hash {}, use both the key and value to the block inside the ||.
details.map {|key,item|"" == item}
=>[false, false, true, false, false]
James Sterling reports on renewable energy developments, climate policy, ecological conservation, and green tech innovations around the globe.
