Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>I came up with a brute force algorithm.<br><br> The algorithm is based on 2 conjectures:<br> <sup>(so it may not work for all matrices - I'll verify them later)</sup></p> <ul> <li>The minimum (number of toggles) solution will contain a specific row or column only once.</li> <li>In whatever order we apply the steps to convert the matrix, we get the same result.</li> </ul> <p><strong>The algorithm:</strong><br> Lets say we have the matrix m = [ [1,0], [0,1] ].</p> <pre><code>m: 1 0 0 1 </code></pre> <p>We generate a list of all row and column numbers,<br> like this: <code>['r0', 'r1', 'c0', 'c1']</code> <br></p> <p>Now we brute force, aka examine, every possible step combinations.<br> For example,<br>we start with 1-step solution,<br> <code>ksubsets = [['r0'], ['r1'], ['c0'], ['c1']]</code> <br><br>if no element is a solution then proceed with 2-step solution,<br> <code>ksubsets = [['r0', 'r1'], ['r0', 'c0'], ['r0', 'c1'], ['r1', 'c0'], ['r1', 'c1'], ['c0', 'c1']]</code></p> <p>etc...</p> <p>A ksubsets element (combo) is a list of toggle steps to apply in a matrix.</p> <hr> <p>Python implementation (tested on version 2.5) <br></p> <pre><code># Recursive definition (+ is the join of sets) # S = {a1, a2, a3, ..., aN} # # ksubsets(S, k) = { # {{a1}+ksubsets({a2,...,aN}, k-1)} + # {{a2}+ksubsets({a3,...,aN}, k-1)} + # {{a3}+ksubsets({a4,...,aN}, k-1)} + # ... } # example: ksubsets([1,2,3], 2) = [[1, 2], [1, 3], [2, 3]] def ksubsets(s, k): if k == 1: return [[e] for e in s] ksubs = [] ss = s[:] for e in s: if len(ss) &lt; k: break ss.remove(e) for x in ksubsets(ss,k-1): l = [e] l.extend(x) ksubs.append(l) return ksubs def toggle_row(m, r): for i in range(len(m[r])): m[r][i] = m[r][i] ^ 1 def toggle_col(m, i): for row in m: row[i] = row[i] ^ 1 def toggle_matrix(m, combos): # example of combos, ['r0', 'r1', 'c3', 'c4'] # 'r0' toggle row 0, 'c3' toggle column 3, etc. import copy k = copy.deepcopy(m) for combo in combos: if combo[0] == 'r': toggle_row(k, int(combo[1:])) else: toggle_col(k, int(combo[1:])) return k def conversion_steps(sM, tM): # Brute force algorithm. # Returns the minimum list of steps to convert sM into tM. rows = len(sM) cols = len(sM[0]) combos = ['r'+str(i) for i in range(rows)] + \ ['c'+str(i) for i in range(cols)] for n in range(0, rows + cols -1): for combo in ksubsets(combos, n +1): if toggle_matrix(sM, combo) == tM: return combo return [] </code></pre> <p>Example:</p> <pre><code>m: 0 0 0 0 0 0 0 0 0 k: 1 1 0 1 1 0 0 0 1 </code></pre> <p><br></p> <pre><code>&gt;&gt;&gt; m = [[0,0,0],[0,0,0],[0,0,0]] &gt;&gt;&gt; k = [[1,1,0],[1,1,0],[0,0,1]] &gt;&gt;&gt; conversion_steps(m, k) ['r0', 'r1', 'c2'] &gt;&gt;&gt; </code></pre>
    singulars
    1. This table or related slice is empty.
    1. POHow to do matrix conversions by row and columns toggles?
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USNick Dandoulakis
    1. USNick Dandoulakis
    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
    1. COThanks.I was never thinking in terms of brute force .Lets see if someone comes with a more efficient solution.
      singulars
      1. PO
      1. USuser160618
 

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