How does Ruby's group_by() method group an array by the identity (or rather self) of its elements?
a = 'abccac'.chars
# => ["a", "b", "c", "c", "a", "c"]
a.group_by(&:???)
# should produce...
# { "a" => ["a", "a"],
# "b" => ["b"],
# "c" => ["c", "c", "c"] }
In a newer Ruby (2.2+?),
a.group_by(&:itself)
In an older one, you still need to do a.group_by { |x| x }
Perhaps, this will help:
a = 'abccac'.chars
a.group_by(&:to_s)
#=> {"a"=>["a", "a"], "b"=>["b"], "c"=>["c", "c", "c"]}
Alternatively, below will also work:
a = 'abccac'.chars
a.group_by(&:dup)
#=> {"a"=>["a", "a"], "b"=>["b"], "c"=>["c", "c", "c"]}
Related
I have this function in Ruby
def translate word
vowels=["a","e","I","O","U"]
i=1.to_i
sentense=word.split(" ").to_a
puts sentense if sentense.length >=1
sentense.split("")
puts sentense
end
I have this phrase "this is a test phrase " and at first I want to create an array that looks like:
["this","is","a", "test", "phrase"]
Then I want to create another array it to look like:
[["t","h","i","s"],["i","s"],["a"],["t","e","s","t"],["p","h","r","a","s","e"].
I tried
sentense=word.split(" ").to_a
new_array=sentense.split("").to_a
but it didn't work
You could use String#split, Enumerable#map and String#chars:
p "this is a test phrase".split.map(&:chars)
# => [["t", "h", "i", "s"], ["i", "s"], ["a"], ["t", "e", "s", "t"], ["p", "h", "r", "a", "s", "e"]]
string.split(' ') could be written as string.split, so you can omit passing the whitespace in parenthesis.
And this also gives you an array, there's no need to use to_a, you'll have an array like ["this", "is", "a", "test", "phrase"], so you can use map to get a new array and for each element inside an array of its characters by using .split('') or .chars.
def chop_up(str)
str.strip.each_char.with_object([[]]) { |c,a| c == ' ' ? (a << []) : a.last << c }
end
chop_up "fee fi fo fum"
#=> [["f", "e", "e"], ["f", "i"], ["f", "o"], ["f", "u", "m"]]
chop_up " fee fi fo fum "
#=> [["f", "e", "e"], ["f", "i"], ["f", "o"], ["f", "u", "m"]]
chop_up "feefifofum "
#=> [["f", "e", "e", "f", "i", "f", "o", "f", "u", "m"]]
chop_up ""
#=> [[]]
With Ruby how do I split on either one of tow conditions -- wheter there are 3 or more spaces or a tab charadter? I tried this
2.4.0 :003 > line = "a\tb\tc"
=> "a\tb\tc"
2.4.0 :004 > line.split(/([[:space:]][[:space:]][[:space:]]+|\t)/)
=> ["a", "\t", "b", "\t", "c"]
but as you can see, the tab character itself is getting included in my results. The results should be
["a", "b", "c"]
What about just split?
p "a\tb\tc".split
# ["a", "b", "c"]
p "a\tb\tc\t\tc\t\t\t\t\t\t\tc\ts\ts\tt".split
# ["a", "b", "c", "c", "c", "s", "s", "t"]
Although that doesn't split when there are three 3 or more white spaces, this might work:
p "a\tb\tc\t\tc\t\t\ t\t\tc\ts\ts\tt".split(/\s{3,}|\t/)
# => ["a", "b", "c", "c", "t", "c", "s", "s", "t"]
line = "aa bb cc\tdd"
line.split /\p{Space}{3,}|\t+/
#⇒ ["aa bb", "cc", "dd"]
This question already has answers here:
How to dynamically create a local variable?
(4 answers)
Closed 7 years ago.
I'm trying to slice an array into equal sizes (rounded down) and save each section to respective variables.
The method each_slice has worked to grab n-sized blocks. However I can't think of a way to:
iterate over the each's blocks' "sub index"
create a new array for each and give each a unique name.
letters = ["a","b","c","d","e","f","g","h","i","j","k","l","m","n"]
def groups_of_five(array)
split_array = array.each_slice(5).to_a
#something like the following:
#array(n) = Array[split_array.each {|x| x}]
end
end
The output I'm hoping for:
groups_of_five(letters)
=> array1: ["a,"b","c","d","e"]
=> array2: ["f","g","h","i","j"]
=> array3: ["k","l","m","n"]
Combine each_slice with with_index and you'll have everything you need:
letters.each_slice(5).with_index(1) do |group, index|
puts "array#{index}: #{group.inspect}"
end
Output is:
array1: ["a", "b", "c", "d", "e"]
array2: ["f", "g", "h", "i", "j"]
array3: ["k", "l", "m", "n"]
It's no longer possible to set local variable dynamically in Ruby versions greather than 1.8, so if you want to assign to variables it will have to be instance variables or you could output a Hash.
The following will create instance variables:
def groups_of_five(array)
array.each_slice(5).with_index(1) do |group, index|
instance_variable_set "#array#{index}".to_sym, group
end
end
groups_of_five(letters)
puts #array1 #=> ["a", "b", "c", "d", "e"]
puts #array2 #=> ["f", "g", "h", "i", "j"]
puts #array3 #=> ["k", "l", "m", "n"]
Or this will output a Hash:
def groups_of_five(array)
hash = {}
array.each_slice(5).with_index(1) do |group, index|
hash["array#{index}".to_sym] = group
end
hash
end
hash = groups_of_five(letters)
puts hash[:array1] #=> ["a", "b", "c", "d", "e"]
puts hash[:array2] #=> ["f", "g", "h", "i", "j"]
puts hash[:array3] #=> ["k", "l", "m", "n"]
If you are looking for a hash structure to return from groups_of_five(letters), here's the solution
def groups_of_five(array)
split_array = letters.each_slice(5).to_a
split_array.reduce({}){ |i,a|
index = split_array.index(a) + 1
i["array#{index}"] = a; i
}
end
# groups_of_five(letters)
#=> {"array1"=>["a", "b", "c", "d", "e"], "array2"=>["f", "g", "h", "i", "j"], "array3"=>["k", "l", "m", "n"]}
You could do this:
def group_em(a,n)
arr = a.dup
(1..(arr.size.to_f/n).ceil).each_with_object({}) { |i,h|
h["array#{i}"] = arr.shift(n) }
end
group_em(letters,1)
#=> {"array1"=>["a"], "array2"=>["b"],...,"array14"=>["n"]}
group_em(letters,2)
#=> {"array1"=>["a", "b"], "array2"=>["c", "d"],...,"array7"=>["m", "n"]}
group_em(letters,5)
#=> {"array1"=>["a", "b", "c", "d", "e"],
# "array2"=>["f", "g", "h", "i", "j"],
# "array3"=>["k", "l", "m", "n"]}
A variant is:
def group_em(arr,n)
(1..(arr.size.to_f/n).ceil).zip(arr.each_slice(n).to_a)
.each_with_object({}) { |(i,a),h| h["array#{i}"]=>a) }
end
I have the following arrays:
passing_grades = ["A", "B", "C", "D"]
student2434 = ["F", "A", "C", "C", "B"]
and I need to verify that all elements in the student array are included in the passing_grades array. In the scenario above, student2434 would return false. But this student:
student777 = ["C", "A", "C", "C", "B"]
would return true. I tried something like:
if student777.include? passing_grades then return true else return false end
without success. Any help is appreciated.
PASSING_GRADES = ["A", "B", "C", "D"]
def passed?(grades)
(grades - PASSING_GRADES).empty?
end
similar to what CDub had but without bug. more readable in my opinion
You could have a method that does the difference of the arrays, and if any results are present, they didn't pass:
PASSING_GRADES = ["A", "B", "C", "D"]
def passed?(grades)
grades.all? {|grade| PASSING_GRADES.include?(grade)}
end
Example:
1.9.3-p484 :117 > student777 = ["C", "A", "C", "C", "B"]
=> ["C", "A", "C", "C", "B"]
1.9.3-p484 :118 > passed?(student777)
=> true
1.9.3-p484 :118 > passed?(student2434)
=> false
I have this:
hash = { "a"=>["a", "b", "c"], "b"=>["b", "c"] }
and I want to get to this: [["a","b","c"],["b","c"]]
This seems like it should work but it doesn't:
hash.each{|key,value| value}
=> {"a"=>["a", "b", "c"], "b"=>["b", "c"]}
Any suggestions?
Also, a bit simpler....
>> hash = { "a"=>["a", "b", "c"], "b"=>["b", "c"] }
=> {"a"=>["a", "b", "c"], "b"=>["b", "c"]}
>> hash.values
=> [["a", "b", "c"], ["b", "c"]]
Ruby doc here
I would use:
hash.map { |key, value| value }
hash.collect { |k, v| v }
#returns [["a", "b", "c"], ["b", "c"]]
Enumerable#collect takes a block, and returns an array of the results of running the block once on every element of the enumerable. So this code just ignores the keys and returns an array of all the values.
The Enumerable module is pretty awesome. Knowing it well can save you lots of time and lots of code.
It is as simple as
hash.values
#=> [["a", "b", "c"], ["b", "c"]]
this will return a new array populated with the values from hash
if you want to store that new array do
array_of_values = hash.values
#=> [["a", "b", "c"], ["b", "c"]]
array_of_values
#=> [["a", "b", "c"], ["b", "c"]]
hash = { :a => ["a", "b", "c"], :b => ["b", "c"] }
hash.values #=> [["a","b","c"],["b","c"]]
There is also this one:
hash = { foo: "bar", baz: "qux" }
hash.map(&:last) #=> ["bar", "qux"]
Why it works:
The & calls to_proc on the object, and passes it as a block to the method.
something {|i| i.foo }
something(&:foo)