How to collect over two arrays then look back to one?

[Peter Booth]

I am reading Ruby for Rails and Ruby Cookbock and delighted by the
Array#find_all and Enumerable#collect methods. I'm wondering what the
idiomatic way to do the following is?

Two parallel arrays A, B . For each element n of A for which f(An) is true,
is g(B[n-3:n+3]) true? Where B[n-3:n+3] refers to seven elements of B whose
position is centered over An' position.

Can the block inside Enumerable#collect know it's position inside the
Enumerable? Can one collect two parallel arrays?

Peter
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[Jason Nordwick]

I think...

a.values_at(*(0...a.size).to_a.select {|i| f(a) && g([i-3,0].max..[i+3,a.size-1].min)})

Ruby seems a little verbose on this one.

-j

 

[William James]

I am reading Ruby for Rails and Ruby Cookbock and delighted by the
Array#find_all and Enumerable#collect methods. I'm wondering what the
idiomatic way to do the following is?

Two parallel arrays A, B . For each element n of A for which f(An) is true,
is g(B[n-3:n+3]) true? Where B[n-3:n+3] refers to seven elements of B whose
position is centered over An' position.

Can the block inside Enumerable#collect know it's position inside the
Enumerable? Can one collect two parallel arrays?

a = Array.new(12) {|i| i*i}
b = Array.new(12) {|i| i*3}
def f(n)
1 == n % 2
end
def g(a)
return false if a.size != 7
0 == a.inject{|p,n| p*n}/a.inject{|s,n| s+n} % 4
end
result = []
a.each_with_index{ |e,i|
result << (f(e) && g( b[i-3 .. i+3] ))
}

 

[dblack]

Hi --

I am reading Ruby for Rails and Ruby Cookbock and delighted by the
Array#find_all and Enumerable#collect methods. I'm wondering what the
idiomatic way to do the following is?

Two parallel arrays A, B . For each element n of A for which f(An) is true,
is g(B[n-3:n+3]) true? Where B[n-3:n+3] refers to seven elements of B whose
position is centered over An' position.

Can the block inside Enumerable#collect know it's position inside the
Enumerable? Can one collect two parallel arrays?

To answer the first question: no. You are free to join Citizens for
map_with_index, of which I am the founder and president


David

--
David A. Black | (e-mail address removed)
Author of "Ruby for Rails" [1] | Ruby/Rails training & consultancy [3]
DABlog (DAB's Weblog) [2] | Co-director, Ruby Central, Inc. [4]
[1] http://www.manning.com/black | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com | [4] http://www.rubycentral.org

 

[Logan Capaldo]

What about Citizens Who Are Happy With enum_with_index.map ? I think they
have a thing-or-two to say on this issue...

-Marshall

Here, here! Down with the giant collection of methods! Up with
higher order methods!