Aggregating Tally counters

问题

Many times I find myself counting occurrences with Tally[ ] and then, once I discarded the original list, having to add (and join) to that counters list the results from another list.

This typically happens when I am counting configurations, occurrences, doing some discrete statistics, etc.

So I defined a very simple but handy function for Tally aggregation:

aggTally[listUnTallied__List:{}, 
         listUnTallied1_List,
         listTallied_List] := 
 Join[Tally@Join[listUnTallied, listUnTallied1], listTallied] //. 
     {a___, {x_, p_}, b___, {x_, q_}, c___} -> {a, {x, p + q}, b, c};

Such that

l = {x, y, z}; lt = Tally@l;
n = {x};
m = {x, y, t};

aggTally[n, {}]
  {{x, 1}}

aggTally[m, n, {}]
  {{x, 2}, {y, 1}, {t, 1}}

aggTally[m, n, lt]
  {{x, 3}, {y, 2}, {t, 1}, {z, 1}}

This function has two problems:

1) Performance

Timing[Fold[aggTally[Range@#2, #1] &, {}, Range[100]];]
  {23.656, Null}
(* functional equivalent to *)
Timing[s = {}; j = 1; While[j < 100, s = aggTally[Range@j, s]; j++]]
  {23.047, Null}

2) It does not validate that the last argument is a real Tallied list or null (less important for me, though)

Is there a simple, elegant, faster and more effective solution? (I understand that these are too many requirements, but wishing is free)

回答1:

Perhaps, this will suit your needs?

aggTallyAlt[listUnTallied__List : {}, listUnTallied1_List, listTallied : {{_, _Integer} ...}] :=
{#[[1, 1]], Total@#[[All, 2]]} & /@ 
       GatherBy[Join[Tally@Join[listUnTallied, listUnTallied1], listTallied], First]

The timings are much better, and there is a pattern-based check on the last arg.

EDIT:

Here is a faster version:

aggTallyAlt1[listUnTallied__List : {}, listUnTallied1_List, listTallied : {{_, _Integer} ...}] :=
Transpose[{#[[All, 1, 1]], Total[#[[All, All, 2]], {2}]}] &@
   GatherBy[Join[Tally@Join[listUnTallied, listUnTallied1], listTallied], First]

The timings for it:

In[39]:= Timing[Fold[aggTallyAlt1[Range@#2, #1] &, {}, Range[100]];]
Timing[s = {}; j = 1; While[j < 100, s = aggTallyAlt1[Range@j, s]; j++]]

Out[39]= {0.015, Null}

Out[40]= {0.016, Null}

回答2:

The following solution is just a small modification of your original function. It applies Sort before using ReplaceRepeated and can thus use a less general replacement pattern which makes it much faster:

aggTally[listUnTallied__List : {}, listUnTallied1_List, 
   listTallied : {{_, _Integer} ...}] := 
  Sort[Join[Tally@Join[listUnTallied, listUnTallied1], 
     listTallied]] //. {a___, {x_, p_}, {x_, q_}, c___} -> {a, {x, p + q}, c};

回答3:

Here's the fastest thing I've come up with yet, (ab)using the tagging available with Sow and Reap:

aggTally5[untallied___List, tallied_List: {}] :=
  Last[Reap[
    Scan[((Sow[#2, #] &) @@@ Tally[#]) &, {untallied}];
    Sow[#2, #] & @@@ tallied;
    , _, {#, Total[#2]} &]]

Not going to win any beauty contests, but it's all about speed, right? =)

回答4:

If you stay purely symbolic, you may try something along the lines of

(Plus @@ Times @@@ Join[#1, #2] /. Plus -> List /. Times -> List) &

for joining tally lists. This is stupid fast but returns something that isn't a tally list, so it needs some work (after which it may not be so fast anymore ;) ).

EDIT: So I've got a working version:

aggT = Replace[(Plus @@ Times @@@ Join[#1, #2] 
                  /. Plus -> List 
                  /. Times[a_, b_] :> List[b, a]), 
                k_Symbol -> List[k, 1], {1}] &;

Using a couple of random symbolic tables I get

a := Tally@b;
b := Table[f[RandomInteger@99 + 1], {i, 100}];

Timing[Fold[aggT[#1, #2] &, a, Table[a, {i, 100}]];]
--> {0.104954, Null}

This version only adds tally lists, doesn't check anything, still returns some integers, and comparing to Leonid's function:

Timing[Fold[aggTallyAlt1[#2, #1] &, a, Table[b, {i, 100}]];]
--> {0.087039, Null}

it's already a couple of seconds slower :-(.

Oh well, nice try.

来源：https://stackoverflow.com/questions/5143575/aggregating-tally-counters

标签

wolfram-mathematica