I have a multidimensional array in ruby like this one:
a = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
How do I add "1" to each element. For instance, I want to end up with something like this:
a = [[2, 3, 4], [5, 6, 7], [8, 9, 10]]
Thanks in advance!
There might be a slightly more clever one liner but this is fairly clear.
a.map { |ar| ar.map { |e| e + 1 } }
Just for fun :
class Array
def increment
map(&:next)
end
end
#Tada!
a.map(&:increment)
a.map { |xs| xs.map(&:succ) }
#=> [[2, 3, 4], [5, 6, 7], [8, 9, 10]]
Related
In ruby I have #each_slice...
(1..10).each_slice(3).to_a
=> [[1, 2, 3], [4, 5, 6], [7, 8, 9], [10]]
I'm looking for an elegant way to do the same in Groovy and this is all I got so far as a beginner:
arr = []
list = (1..10) as Queue
while(!list.isEmpty()) {
sub_arr = []
3.times { sub_arr << list.poll() }
sub_arr.removeAll([null])
arr << sub_arr
}
arr
Result: [[1, 2, 3], [4, 5, 6], [7, 8, 9], [10]]
You need collate in groovy
(1..10).collate(3)
I am trying to conceptualize the iteration of two loops
numbers_array = [1,2,3,4,5,6,7,8,9,10]
add_to_array = [1,2,3,4]
While the numbers_array iterates, add_to_array iterates simultaneously adding both elements together at the same time. The caveat is once add_to_array reaches the end, it starts over adding its element to the next index in numbers_array. So at numbers_array[4] we would be adding add_to_array[0] then adding numbers_array[5] to add_to_array[1] and so on. This process would repeat until we reach the end of the numbers_array.
Any input would be greatly appreciated!
You are looking for Enumerable#zip and Enumerable#cycle:
numbers_array = [1,2,3,4,5,6,7,8,9,10]
#⇒ [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
add_to_array = [1,2,3,4]
#⇒ [1, 2, 3, 4]
numbers_array.zip(add_to_array.cycle)
#⇒ [[1, 1], [2, 2], [3, 3], [4, 4], [5, 1],
# [6, 2], [7, 3], [8, 4], [9, 1], [10, 2]]
Now do whatever you want with the array returned. E.g. to reduce the zipped result summing elements, map ro Enumerable#sum:
numbers_array.zip(add_to_array.cycle).map(&:sum)
#⇒ [2, 4, 6, 8, 6, 8, 10, 12, 10, 12]
It works by using the % operator to cycle through the indexes.
numbers_array = [1,2,3,4,5,6,7,8,9,10]
add_to_array = [1,2,3,4]
numbers_array.map.with_index do |n, i|
n + add_to_array[i % add_to_array.length]
end
A cool method that's similar, if you didn't want to start over at the next array, would be .zip
https://apidock.com/ruby/Array/zip
add_to_array.zip(*numbers_array.each_slice(add_to_array.size)).
map { |a| a.sum { |e| e.to_i } }
#=> [16, 20, 13, 16]
e.to_i is needed to convert nil values to zeros. See NilClass#to_i.
Another option:
numbers_array.map { |e| e + add_to_array.rotate!.last }
# => [2, 4, 6, 8, 6, 8, 10, 12, 10, 12]
Drawback: add_to_array is mutated by rotate!
I am looking for a way to perform a certain operation (for instance delete_if) on an array and return both the deleted elements, and the remaining elements.
For example
a = [1,2,3,4,5,6,7,8,9,10]
a.delete_if {|x| x.even? } #=> [[1, 3, 5, 7, 9]]
But what I am looking for is something like
a = [1,2,3,4,5,6,7,8,9,10]
a.some_operation #=> [[1,3,5,7,9],[2,4,6,8,10]]
How would I go about doing this?
Using Enumerable#partition:
a = [1,2,3,4,5,6,7,8,9,10]
a.partition &:even?
# => [[2, 4, 6, 8, 10], [1, 3, 5, 7, 9]]
The first element of the Enumerable#partition return value contains the elements that are evaluated to true in the block. So you need to use odd? to get what you want.
a.partition &:odd?
# => [[1, 3, 5, 7, 9], [2, 4, 6, 8, 10]]
You might be looking for something like this:
a = [1,2,3,4,5,6,7,8,9,10]
a.group_by { |x| x.even? }.values
#=> [[1, 3, 5, 7, 9], [2, 4, 6, 8, 10]]
I have several equally sized arrays containing numbers (matrix), and I want to sum them all by their index (matrix columns).
For example, if I have:
data = [[1, 2, 3, 4], [5, 6, 7, 8]]
I want to get the result:
column_totals = [6, 8, 10, 12]
I understand how to do this imperatively, but how would I do this using functional programming? (Preferably, using built in Enumerable methods.) I wasn't very happy with any of the functional solutions I came up with.
I ended up using the Matrix class:
require 'matrix'
data = [[1, 2, 3, 4], [5, 6, 7, 8]]
matrix = Matrix[*data]
# Added sum method to Vector class.
matrix.column_vectors.map { |column| column.sum }
I'm happy enough with that solution, but am frustrated that I couldn't wrap my mind around a good functional solution without relying on the Matrix class.
Specifically, I was tripped up on the step to transform this:
data = [[1, 2, 3, 4], [5, 6, 7, 8]]
into this:
columns = [[1, 5], [2, 6], [3, 7], [4, 8]]
Any reason to not use Array#transpose?
data.transpose
# => [[1, 5], [2, 6], [3, 7], [4, 8]]
Alternatively, if you only want to use Enumerable methods to iterate, you can do
columns = data.inject(Array.new(data.first.length){[]}) { |matrix,row|
row.each_with_index { |e,i| matrix[i] << e }
matrix }
# => [[1, 5], [2, 6], [3, 7], [4, 8]]
or
columns = data.flatten.group_by.with_index { |e,i| i % data[0].size }.values
# => [[1, 5], [2, 6], [3, 7], [4, 8]]
To sum:
columns.map { |row| row.inject :+ }
# => [6, 8, 10, 12]
Thirdly, if you don't need the intermediate columns:
data.inject { |s,r| s.zip(r).map { |p| p.inject :+ } }
# => [6, 8, 10, 12]
You could use Array#transpose, as #Matt hinted, and then sum the arrays inside:
data.transpose.map {|a| a.reduce(:+) }
I am trying to find sum of each array.
(1..9).to_a.combination(3).to_a.each{ |item| item.inject{:+}}
But my code gives the followings.
[[1, 2, 3], [1, 2, 4], [1, 2, 5], [1, 2, 6], [1, 2, 7], [1, 2, 8], [1, 2, 9],
[1, 3, 4], [1, 3, 5], [1, 3, 6], [1, 3, 7], [1, 3, 8], ...
What I am expecting is something like this.
[6, 7, 8, 9,...]
How can I find sum of each array?
You are very close, a little change on your code may help:
(1..9).to_a.combination(3).map { |a| a.inject(:+) }
(1..9).to_a.combination(3).to_a.map { |item| item.inject(:+) }
I found another way with #reduce.
(1..9).to_a.combination(3).map { |item| item.reduce(:+) }