Array loops: new thread

I thought it would be better to start a new thread for my current
issue, since the old one is filled with code in various stages.
Apologies. Gives me a chance to ask more succinctly regarding the
core issue.

This is just an example.
I have 2 arrays

firstarray = [‘1’,'2,‘3’,‘4’,‘5’]
secondarray = [‘1’,‘2’,‘3’,‘4’,‘5’,‘6’,‘7’]

I’m looping through firstarray.each do |x|
go through some blocks. At some point, either the start of the outter
array or somewhere down in the conditional statements I need to find
out if elements of firstarray are in secondarray. The only way I can
fathom doing this right now is by starting another loop, i.e.
secondarray.each do |y|. Problem is this seems to create constant
problems where the outter loop / [0] element is going through the
entire inner loop before proceeding on. to it’s next element. Maybe
as someone suggested earlier today to me, to use break. Haven’t had
much luck with that yet.

If this question makes sense, anyone have some suggestions , comments
or anything else that might be helpful ?

TIA
Stuart

If you just need to see if an element is contained in an array try
this…

secondarray.include?( ‘5’ )
=> true

mark

On Tue, Jul 04, 2006 at 03:27:07AM +0900, Dark A. wrote:

If this question makes sense, anyone have some suggestions , comments
or anything else that might be helpful ?

TIA
Stuart

How about something like:

secondarray.each do |x|
if firstarray.include?(x)
// do something
end
end

Brian

On Jul 3, 2006, at 19:27, Dark A. wrote:

I’m looping through firstarray.each do |x|
go through some blocks. At some point, either the start of the outter
array or somewhere down in the conditional statements I need to find
out if elements of firstarray are in secondarray. The only way I can
fathom doing this right now is by starting another loop, i.e.
secondarray.each do |y|. Problem is this seems to create constant
problems where the outter loop / [0] element is going through the
entire inner loop before proceeding on. to it’s next element. Maybe
as someone suggested earlier today to me, to use break. Haven’t had
much luck with that yet.

If you don’t want to use loops at all, you could use the intersection
operator:

overlap = firstarray & secondarray

If you do want to use loops (which would be good practice for you),
then just be careful to remember what each loop is doing. While
using include? or the intersection operator wouldn’t hurt anything,
given your trouble with nesting loops it’s probably good practice to
learn how to do them properly - they’re an incredibly common
construct in programming, and if you don’t learn how to build them
for something simple you could get very stuck later on. Even your
simple file comparison example wouldn’t work using include?, since
the filenames include different directories.

The basic idea you should remember is that you can write the inner
loop as if it were a normal loop working with a single variable. For
example, if the outer loop is “firstarray.each do |first|” then you
can write the inner loop as if you had this:

first = 1
secondarray.each do |second|

do things with first and second here.

end

Here’s a simple example which tells you exactly what it’s doing:

firstarray = [1, 2, 3]
secondarray = [1, 3, 5]
overlap = []
firstarray.each do |first|
puts “Outer loop setting first = #{first}”

we want to compare first to everything in the second array:

secondarray.each do |second|
puts “\tInner loop setting second = #{second}”
print “\tComparing #{first} to #{second}…”
if first == second
puts “matched!”
# do what we need to when we find a match
overlap.push(first)
# if you know there’s a max of 1 match,
# you could put a break here to stop looking
# for more matches.
else
puts “no match.”
end
end
puts “\tInner loop finished.”
end
puts “Outer loop finished.”
puts overlap

matthew smillie.

Cool guys, thank you. I was not aware of include and had just gone
down the array class instance methods prior to asking for help. Leads
me to conclude I should have read through it 3x not once.

Stuart

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