Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>If you assume that all values in the array are digits in a base-n numbering system where n is the length of the array, the k-th combination will be the equivalent of k expressed in base-n.</p> <p>If you are wanting to start with a given combination (i.e. [1,6,5]) and continue from there, simply read this starting point as a number in base-n. You can then start iterating through successive combinations by incrementing.</p> <p>EDIT: Further explanation:</p> <p>Let's start with the array. The array contains 6 values, so we are working in base-6. We will assume the index of each element in the array is the element's base-6 value.</p> <p>Values in base-6 range from 0 to 5. This may get confusing because our example uses digits, but we could do this with combinations of anything. I will put 'quote' marks around the digits we are combining.</p> <p>Given a combination ['1', '6', '5'], we first need to convert this to a base-6 value. '1' becomes 0, '6' becomes 5 and '5' becomes 4. Using their positions in the starting value as their powers in base-6, we get:</p> <p>(0 * 6^0) + (5 * 6^1) + (4 * 6^2) = 174 (decimal)</p> <p>If we want to know the next combination, we can add 1. If we want to know 20 combinations ahead, we add 20. We can also subtract to go backwards. Let's add 1 to 174 and convert it back to base-6:</p> <p>175 (decimal) = (1 + 6^0) + (5 * 6^1) + (4 * 6^2) = 451 (base-6) = ['2', '6', '5'] (combination)</p> <p>For more on number bases, see <a href="http://en.wikipedia.org/wiki/Radix" rel="nofollow">http://en.wikipedia.org/wiki/Radix</a> and <a href="http://en.wikipedia.org/wiki/Base_%28exponentiation%29" rel="nofollow">http://en.wikipedia.org/wiki/Base_%28exponentiation%29</a></p>
    singulars
    1. This table or related slice is empty.
    1. POGenerate kth combination without generating/iterating previous
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USCentijo
    1. USCentijo
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. COAs mentioned in the answer by Mario Rossi, my math isn't so good and I'm having trouble following this. Is this answer essentially the same as Mario's?
      singulars
      1. PO
      1. USJeffThompson
    2. COMy answer is a general case for finding permutations. Mario's answer is specific to itertools.
      singulars
      1. PO
      1. USCentijo
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload