I'm working with Ripper sexp expressions, it looks like this:
[:program,
[[:class,
[:const_ref, [:#const, "A", [1, 6]]],
nil,
[:bodystmt,
[[:class,
[:const_ref, [:#const, "B", [1, 15]]],
nil,
[:bodystmt,
[[:def,
[:#ident, "test", [1, 22]],
[:params, nil, nil, nil, nil, nil],
[:bodystmt, [[:void_stmt]], nil, nil, nil]]],
nil,
nil,
nil]]],
nil,
nil,
nil]]]]
And i'm using array as path to get element in sexp expression. For example
path = [1,0,1,1] => sexp[1][0][1][1]
will get me
[:#const, "A", [1, 6]]
With this path I can get next, previous, parent elements and so on.
But I'm wondering is there a data structure which more suitable for this kind of tasks?
Besides the obvious trees, you may want to look at zippers:
http://en.wikipedia.org/wiki/Zipper_(data_structure)
Someone recently implemented form-zip for Clojure, if you want to look at an example:
https://github.com/GeorgeJahad/form-zip
Related
I have the following:
input string = "1234"
output new_array should = [12, 3, 4, 34]
def string_to_array(string)
noun = ["d", "fgh", "i", "jk", "bcd", "cdef"]
verb = ["cd", "ef", "f", "jkl", "abc"]
ary = (noun+verb).select { |s| string.include? s }
ary.unshift(ary.delete(string)).compact
end
string = "cdef"
string_to_array(string) #=> ["cdef", "d", "cd", "ef", "f"]
I used Array#select, Array#+, Array#delete, Array#unshift, Array#compact and String#include?.
If you want to remove duplicate from output array, use Array#uniq
You could use String#scan (see the last sentence of the doc especially) together with a regular expression. My objective is to demonstrate this approach, not to suggest that it should be the preferred approach.
nouns = ["cdef", "d", "fgh", "i", "jk", "bcd"]
verbs = ["cd", "ef", "f", "jkl", "abc"]
R = Regexp.new (nouns+verbs).map { |s| "(?=(#{s}))?" }.join
#=> /(?=(cdef))?(?=(d))?(?=(fgh))?(?=(i))?(?=(jk))?(?=(bcd))?(?=(cd))?(?=(ef))?(?=(f))?(?=(jkl))?(?=(abc))?/
def string_to_array(str, nouns, strings)
str.scan(R).flatten.compact
end
str = "cdef"
string_to_array(str, nouns, verbs)
#=> ["cdef", "cd", "d", "ef", "f"]
Note:
str.scan(R)
#=> [["cdef", nil, nil, nil, nil, nil, "cd", nil, nil, nil, nil],
# [nil, "d", nil, nil, nil, nil, nil, nil, nil, nil, nil],
# [nil, nil, nil, nil, nil, nil, nil, "ef", nil, nil, nil],
# [nil, nil, nil, nil, nil, nil, nil, nil, "f", nil, nil],
# [nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil]]
(?=(cdef))? ((?=(cdef)?) also works) is a positive lookahead enclosed in a capture group. It requires that a particular location in the string is immediately followed by the content of the lookahead, but is not part of the match itself. The question mark makes the lookahead optional.
This question already has answers here:
Creating matrix with `Array.new(n, Array.new)`
(2 answers)
Closed 5 years ago.
Context: Im trying to populate a 2D array with while loops ,after witch I want to try and do it with {} block format. The point is to understand how these two syntax structures can do the same thing.
I have been reviewing this code and scouring the internet for the past hour and Ive decided that I'm simply not getting something, but I dont understand what that is.
The outcome should be
=> [["A1", "A2", "A3", "A4", "A5", "A6", "A7", "A8"]
=> ..(Sequentially)..
=>["H1", "H2", "H3", "H4", "H5", "H6", "H7", "H8"]]
The code is as follows:
char= ('A'..'H').to_a
num= (1..8).to_a
arr=Array.new(8,Array.new(8))
x=0
while x <8
y=0
while y < 8
arr[x][y] = char[x] + num[y].to_s
y+=1
end
x+=1
end
arr
Thank you in advance, I appreciate your patience and time.
####Edit####
The source of the confusion was due to a lack of understanding of the reference concept. Referencing allows us, by using the Array.new(n,Array.new(n)) method scheme, to access the values of the nested arrays that share a reference to their data via their parent array. This question is addressed directly here: Creating matrix with `Array.new(n, Array.new)` . Although I thought it was a issue with my while loops, the problem was indeed how I created the matrix.
Your code is not working due to call to reference. Ruby is pass-by-value, but all the values are references. https://stackoverflow.com/a/1872159/3759158
Have a look at the output
2.4.3 :087 > arr = Array.new(8,Array.new(8))
=> [[nil, nil, nil, nil, nil, nil, nil, nil], [nil, nil, nil, nil, nil, nil, nil, nil], [nil, nil, nil, nil, nil, nil, nil, nil], [nil, nil, nil, nil, nil, nil, nil, nil], [nil, nil, nil, nil, nil, nil, nil, nil], [nil, nil, nil, nil, nil, nil, nil, nil], [nil, nil, nil, nil, nil, nil, nil, nil], [nil, nil, nil, nil, nil, nil, nil, nil]]
2.4.3 :088 > arr[0][0] = 'B'
=> "B"
2.4.3 :089 > arr
=> [["B", nil, nil, nil, nil, nil, nil, nil], ["B", nil, nil, nil, nil, nil, nil, nil], ["B", nil, nil, nil, nil, nil, nil, nil], ["B", nil, nil, nil, nil, nil, nil, nil], ["B", nil, nil, nil, nil, nil, nil, nil], ["B", nil, nil, nil, nil, nil, nil, nil], ["B", nil, nil, nil, nil, nil, nil, nil], ["B", nil, nil, nil, nil, nil, nil, nil]]
This is happen because of call by object on array object you can see this in effect by a simple example
a = []
b = a
b << 10
puts a => [10]
and very same thing is happening with your code.
Instead of all that try this :
('A'..'H').map{|alph| (1..8).map{|num| "#{alph}#{num}"}}
I have an integer with a value
I want to create an array with nil values representing this integer
For example:
i = 5
# The result i want is
[nil, nil, nil, nil, nil]
What is the most Ruby way of doing this? Aka, the shortest way. Without need of looping et c.
This is very basic question:
i = 5
Array.new(i) #=> [nil, nil, nil, nil, nil]
i = 5
[nil]*i #=> [nil, nil, nil, nil, nil]
I have built a presenter class whose only job is to convert a given array into a string. I am test driving the solution, so I started with "[nil, nil, nil]" but each nil will eventually be replaced with letter. That functionality is being handled by another class.
I am trying now to build an interface whose only job is to convert that string back to an array. So I will need to convert e.g. "[\"a\", \"b\", nil]" back to ["a", "b", nil]. But I am stuck.
For example, I'd like to convert
"[nil, nil, nil]"
to
[nil, nil, nil]
How could I do it?
Just use:
eval(string)
eval("[nil, nil, nil]")
Caution:
This is a very insecure method and you have to use it only if you are completely sure that the string contains a SAFE array..
I am guessing that you are producing the string yourself on one side, for example:
arr = [nil, nil, nil]
str = arr.inspect
#=> "[nil, nil, nil]"
Whereas I would advise you to serialize the array using a format such as JSON, YAML or Ruby's built in Marshalling library.
JSON
require 'json'
arr = [nil, nil, nil]
str = JSON.dump(arr)
#=> "[null,null,null]"
JSON.load(str)
#=> [nil, nil, nil]
YAML
require 'yaml'
arr = [nil, nil, nil]
str = YAML.dump(arr)
#=> "---\n- \n- \n- \n"
YAML.load(str)
#=> [nil, nil, nil]
Marshal
arr = [nil, nil, nil]
str = Marshal.dump(arr)
#=> "\x04\b[\b000"
Marshal.load(str)
#=> [nil, nil, nil]
I'm experiencing the following. I expect only the first sub-element of the first sub array to be assigned "x", not the first element of each sub array. Can anyone explain this behaviour, and perhaps how to work around it? (Note that this may well be expected behaviour, but if it is, it contradicts my expectations.)
x = Array.new(3, Array.new(5))
# => [[nil, nil, nil, nil, nil], [nil, nil, nil, nil, nil], [nil, nil, nil, nil, nil]]
x[0][0] # => nil
x[0][0] = "x"
x
# => [["x", nil, nil, nil, nil], ["x", nil, nil, nil, nil], ["x", nil, nil, nil, nil]]
workaround is :
x = Array.new(3) { Array.new(5) }
x[0][0] = 'a'
x # => [["a", nil, nil, nil, nil], [nil, nil, nil, nil, nil], [nil, nil, nil, nil, nil]]
new(size) {|index| block }
Here an array of the given size is created. Each element in this array is created by passing the element’s index to the given block and storing the return value.
Read also Common gotchas
When sending the second parameter, the same object will be used as the value for all the array elements. Since all the Array elements store the same array Array.new(5), changes to one of them will affect them all.
If multiple copies are what you want, you should use the block version which uses the result of that block each time an element of the array needs to be initialized, as I did above.
2d_array = Array.new(rows) { Array.new(columns) }