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arrays ruby and combinations
Posted: Sat Jun 21, 2014 5:08 pm
by tester
On ruby website there is something like this:
Code: Select all
Examples:
a = [1, 2, 3, 4]
...
a.combination(2).to_a #=> [[1,2],[1,3],[1,4],[2,3],[2,4],[3,4]]
...
What I'd like to do is this.
First array to push trough combinatorics is made of numbers.
I'd like to get unique midpoints according to formula (A+B)/2.
If the array is:
100
200
300
then the output list would be something like this:
150
200
250
Second array to push through combinatorics is made of strings.
I'd like to get a list of combined strings that looks like this: A-B
If the array of string names is:
A
B
C
then the output list would be something like this:
A-B
A-C
B-C
I refer to combinatorics, because order between two arrays is important (i.e. names and their numbers).
How to make it?
Re: arrays ruby and combinations
Posted: Sat Jun 21, 2014 5:52 pm
by trogluddite
Wierd, never noticed that this one returned an 'Enumerator' instead of Array.
But handy, because '.map' can immediately follow without needing to convert to array in the middle - should be very fast!
NB) If you need exact 1 to 1 correlation between index of mid-points and index of Strings, remove '.uniq' - it will remove identical values, maybe leaving the number array shorter than the String array.
Re: arrays ruby and combinations
Posted: Sat Jun 21, 2014 10:47 pm
by tester
The string array must be exact to the array of numbers. By "unique" I meant unique index combinations (i.e. to avoid Ato B and B to A). In this step - output numbers refer to midpoint descriptions. Thanks!
Re: arrays ruby and combinations
Posted: Sun Jun 22, 2014 12:37 am
by tester
Okay, question for step 2. Similar thing as above, but now we have two separate arrays of numbers and two separate arrays of descriptors.
What I would like to do here - is to combine each element from array 1 with each element from array 2.
It would be like this
Text arrays:
A
B
C
D
E
results in
A-B
A-C
A-D
B-C
B-D
B-E
And numeric arrays go in the same way, just by the equation: x - y.
So the end result - are two synchronized arrays, one with descriptors, one with calculated data.
How to make this one?
For the rest of things (picking indexes for values in specified range), I think I have working modules somewhere around.
Re: arrays ruby and combinations
Posted: Sun Jun 22, 2014 4:08 pm
by tester
A little help here please.
Re: arrays ruby and combinations
Posted: Sun Jun 22, 2014 7:52 pm
by trogluddite
I think this is right - I'm guessing that "A-B, A-C, A-D" is a typo - should be "A-C, A-D, A-E". If not, I'm not quite sure how to make sense of the specification...
Re: arrays ruby and combinations
Posted: Sun Jun 22, 2014 7:59 pm
by tester
Yes, it was my mistake (long night; playing with new i-crap device since few days; the longer I have it the more I think I start do programming for them, but not because I like them - lack of apps that I would like to use...).
Thanks!