MATLAB: Sorting Variables by Value

sortvariables

I have a series of solved values I'd like to have sorted. For example,

Apple = (Apple_weight in pounds) / 2.2

Bannana = (Bannana_weight in pounds) / 2.2

Orange = (Orange_weight in pounds) / 2.2

I'd like to have these sorted by mass. In this case it doesn't matter what the mass of the apple is, just whether it is more or less than an orange. How do I get back Orange, Apple, Bannana?

*Side note: I really wish Matlab handled units*

Best Answer

You read about sort. Great. READ ALL ABOUT SORT. And get used to working with arrays, with vectors, rather than named variables, with each data point in a separate variable. MATLAB is a language that uses matrices. Things work better in MATLAB once you start to use vectors and matrices, because now you can work on an entire set of data in one operation.

fruitnames = {'Apple', 'Banana', 'Orange'};
% Just some random numbers, since I don't have a scale handy, nor an orange
% So these are just wild guesses at the weight in pounds of some phantasmic fruits
fruitweight = [.5 .4 .6];
fruitmass = fruitweight/2.205; % 2.205 pounds is roughly one kilogram mass on earth
[~,sortind] = sort(fruitmass,'descend');
fruitnames(sortind)
ans =
  1×3 cell array
    {'Orange'}    {'Apple'}    {'Banana'}

And since it is now almost time for breakfast here, all this talk about fruit is making me hungry. :) Thankfully, we have both apples and bananas available at home today, so I'll even have a choice.

Related Solutions

MATLAB: How do you get multiple minimum values in a column based on grouping and then isolate the corresponding rows for the whole table

[g,ig]=findgroups(data.names);
b=splitapply(@(x) {maxk(x,10)},data.age,g);

b contains the k oldest elements for each group...you'll have to use an m-file function to return the optional second index from maxk to locate the position of the N individuals in the group.

>> [cellstr(ig) b]
ans =
  7×2 cell array
    {'Ben'  }    {10×1 double}
    {'Billy'}    { 4×1 double}
    {'Happy'}    { 4×1 double}
    {'Jenny'}    {10×1 double}
    {'Joe'  }    { 8×1 double}
    {'Kate' }    {10×1 double}
    {'Smith'}    {10×1 double}
>>

ADDENDUM: The indexing would look something like--

function [mx,ix]=getmaxk(x,n)
% wrapper for maxk cuz can't return second output w/ anonymous function
  [mx,ix]=maxk(x,n);
  mx={mx};
  ix={ix};
end
fnmaxk=@(x) getmaxk(x,10);
[b,ib]=splitapply(fnmaxk,data.age,g);

ADDENDUM SECOND:

OK, it's not so bad after all -- have to do it explicitly right now; seems like a good candidate for an enhancement to splitapply() to have available as an auxiliary variable.

Start with

function sq=getmaxkgrp(x,v)
% returns the group variable sequence associated with the n maxk values of x
  n=10;
  [mx,ix]=maxk(x,n);
  sq=v(ix);
end

which has the 10 value hardcoded; you can use the indirect method illustrated above to be able to change the number for which you're looking.

Then, as suggested, augment the table with

data.seq=[1:height(data)].';        % add the sequence number in table of each row
ix=splitapply(@(x1,x2) {getmaxkgrp(x1,x2)},data.age,data.seq,g);  % and return that seq number for the top n
tmaxk=(cellfun(@(ix) data(ix,1:end-1),ix,'uni',0));  % retrieve those records from full table
tmaxk=vertcat(tmaxk{:});                             % and combine into a table

Above results in--

>> tmaxk =
  56×3 table
    names    age    pet 
    _____    ___    ____
    Ben      31     fish
    Ben      31     bird
    Ben      31     bird
    Ben      31     bird
    Ben      31     fish
    Ben      21     dog 
    Ben      21     fish
    Ben      21     dog 
    Ben      21     fish
    Ben      17     dog 
    Billy    30     fish
    Billy    30     bird
    Billy    30     fish
    Billy    30     bird
    Happy    31     bird
    Happy    31     cat 
    Happy    31     bird
    Happy    31     cat 
    Jenny    30     cat 
    Jenny    30     dog 
    Jenny    30     dog 
    Jenny    30     fish
    Jenny    30     dog 
    Jenny    30     fish
    Jenny    30     dog 
    Jenny    30     fish
    Jenny    30     cat 
    Jenny    30     dog 
    Joe      79     dog 
    Joe      79     dog 
    Joe      21     dog 
    Joe      20     cat 
    Joe      19     cat 
    Joe      18     bird
    Joe      15     cat 
    Joe      15     cat 
    Kate     60     fish
    Kate     60     fish
    Kate     60     fish
    Kate     51     fish
    Kate     51     fish
    Kate     51     fish
    Kate     51     fish
    Kate     50     bird
    Kate     50     dog 
    Kate     50     bird
    Smith    38     fish
    Smith    38     bird
    Smith    38     fish
    Smith    38     bird
    Smith    38     bird
    Smith    38     fish
    Smith    30     bird
    Smith    29     bird
    Smith    29     cat 
    Smith    29     cat 
>>

I didn't test it extensively but I believe it will have returned the correct values. Using a smaller value for N would make that part much easier; left as "Exercise for Student!" :)

MATLAB: Sortrows not working with logical column

The doc at the link is addressing an array input which array can be one of the various types listed. It isn't describing a cell array. It appears, in fact, the documentation, while giving an example for a cell array of string values, doesn't address cell array inputs at all in the input description.

Hence, not sure it can be called a bug but appears to be a quality of implementation failure, for sure.

Looks like the workaround will be to either cast the logical to a numeric value before sorting or convert the cell array to a table and sortrows it--I'm guessing that would work.

I would submit a bug report, though...at least make TMW commit on what it is supposed to do.

ADDENDUM

Well, after the earlier comments, turns out we can go further and it can undoubtedly be made to work...the wrapper around the mex guts routines that do the bulk of the work is an m-file so can (at least thru R2014b here) see what's going on...in the end one gets to the following in the internal function sort_cell_back_to_front that is the one that errors.

if ~isempty(x)
  for k = n:-1:1
    if isnumeric(x{1, k})
      ...error test for array cell content elided for clarity in function...
      tmp = cell2mat(x(ndx, k));
      ind = sortrowsc(tmp, col(k));
      ndx = ndx(ind);
    else
      tmp = char(x(ndx,k));
      ind = sortrowsc(tmp, sign(col(k))*(1:size(tmp,2)));
      ndx = ndx(ind);
    end
  end

and we see that since a LOGICAL is not numeric, it's going to be treated as string. Fixing up this test in a copy of sortrows might correct the issue. I'd suggest pasting this code snippet with the bug report.

ADDENDUM 2

I tried the simple expedient of

        if isnumeric(x{1, k}) || islogical(x{1, k})

but it then errored on the subsequent cell2mat line with mixed types inside cell2mat. I don't have sufficient time at the moment to try to delve more deeply into the guts to work on a fixup, but that's where the issues are, anyways.

You can try to either patch this or use the workaround of making the type change or use table that may be more robust; not sure on that count. Well, let's just try and see...

>> res=table2cell(sortrows(cell2table(TCRes),-2));
>>

does seem to work ok. It didn't seem to take long for your dataset size to create the table and doing it as above makes it a temporary so doesn't clutter up workspace afterwards. The additional conversion back to cell didn't seem to take a reliably measurable additional amount of time over that without. If datasets got really large possibly...

The base case still deserves a bug report probably, but TMW may not treat it with great urgency...

ADDENDUM 3

I had a few minutes to look at this a little more--seemed puzzling that the above fixup failed on mixed metaphors so I dug into the dataset you supplied a little more...first try out of the box croaks--

>> tmp=cell2mat(TCRes(:,2));
Error using cell2mat (line 45)
All contents of the input cell array must be of the same data type. 
>>

So, the error in the modified sortrows really isn't anything to do with it at all...

So, let's just look at the elements--

>> cellfun(@(x) x,TCRes(:,2));
Error using cellfun
Mismatch in type of outputs, at index 16, output 1 (logical versus double).
Set 'UniformOutput' to false. 
>>

Your data are corrupt; the 16th value is a double instead of logical, how many more?

>> sum(cellfun(@islogical,arrayfun(@(x) x,TCRes(:,2))))
ans =
 554
>>

so there are 16 bad apples in the barrel. Fixing those and the above code change likely will then work.

IN FINE

>> idx=find(cellfun(@isnumeric,arrayfun(@(x) x,TCRes(:,2))))'
idx =
  16    54    92   130   168   206   244   282   320   358   396   434   472   510   548   552
>> diff(idx)
ans =
  38    38    38    38    38    38    38    38    38    38    38    38    38    38     4
>>

It looks like whatever logic you used to build the array has some regularity in setting values and every 38th after the 16th plus the last is a double instead of logical. This is a bug in your code logic that needs fixing.

With that and the change to sortrows noted above, then the "classic" sortrows works on your cell array.

>> for i=1:length(idx),TCPRes(idx(i),2)={logical(TCPRes{idx(i),2})};end
>> out=sortrows(TCPRes,-2);
>>

after the aforementioned code change. I made local copy to alias the original for the test; I'd recommend if you choose to go this route to make a copy of the original and name it something else.

Best Answer

Related Solutions

MATLAB: How do you get multiple minimum values in a column based on grouping and then isolate the corresponding rows for the whole table

MATLAB: Sortrows not working with logical column

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