Generate array of limited combinations from another array

Question

I need to generate 2D array in rails from a set of given strings. For example:

days =[ "Monday",
     "Tuesday",
     "Wednesday",
  ]

Now I want to create a 2D array and the data in this array will be fill by using days string in random manner.

Example:

[monday, tuesday, wednesday],
[tuesday, wednesday, monday]
...

and so on depends on given dimensions

How to do it?

Edit

I tried this

# global variable
@@test_array = %w(:sunday :monday :tuesday)

def get_data(row, col)
 @data_field =  @@test_array.permutation.to_a(col)
return @data_field.slice!(row)

If I pass row:1 and col:1 It is working but If i pass a big number like 20 in rows and column it is storing null in database.

Edit-2

days = ["monday, "tuesday"]
rows = 3
col = 3

It should return (one of the possible solution due to random generation)

[[monday, tuesday, monday],[tuesday, monday, tuesday], [monday, monday, tuesday]]

souslov · Accepted Answer · 2015-06-28 03:02:18Z

2

You can use Array#permutation if you don't want repetetions in the subarrays.

col¹ ∈ [1; 3]
row² ∈ [0; 3]

days.permutation(col).to_a.slice(0, row)

Demonstration

If you want repetitions in the subarrays, you can use Array#repeated_permutation.

col ∈ [1; 3]
row ∈ [0; 3³(= 27)]:

days.repeated_permutation(col).to_a.slice(0, row)

Demonstration

If you want repetitions in the subarrays and also expand your column number to the custom, independent from length of the original array number, you can use Array#repeated_combination.

col ∈ [1; ∞³ )
row ∈ [0; col^col]:

days.repeated_combination(col).to_a.slice(0, row)

Demonstration

¹ col is the number of elements in each subarray.
² row is the number of subarrays in the desired 2D array.
³ The upper bound is specified as ∞ to represent that this value is not bounded by the length of the original array.

edited Jun 28, 2015 at 3:02

answered Jun 28, 2015 at 0:06

souslov

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6 Comments

Amit Pal Over a year ago

Thanks! But where can i apply the limit of rows and column?

souslov Over a year ago

@AmitPal: Well, with specified argument from 1 to the length you can control the number of columns, the number of rows can be cut off with slice method.

souslov Over a year ago

@AmitPal: Well, as I said, you can specify argument from 1 to length, in your case, from 1 to 3. It is all about possible combinations, you can't build 20 different combinations from 3 values – 3! = 3*2*1 = 6. So, you can have maximum 2d array of 3x6 and minimum of 1x1( or just empty array, if it counts).

Amit Pal Over a year ago

I think you misunderstood me. I wanted to generate a matrix from the set of given string with a given dimension. Please have a look at the Edit-2 section

Amit Pal Over a year ago

Let us continue this discussion in chat.

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