MATLAB: How to compare strings and create a new column with the comparison result

columnscomparecreatenew columnstrings

I have "cat1" and "cat2" that are 2 columns with strings:

If cat1 is low and cat2 is low, I want cat3 to be '1'; If cat1 is medium low and cat2 is medium low, I want cat3 to be '2'; And so on until high and high. If none of these conditions are satisfied, I want cat3 to be '0';

How can I do this? I tried this way but it says "Undefined operator '==' for input arguments of type 'cell'" :

teste1 = repmat( {''}, length(catpreco(:,1)), 1);
mask = catpreco(:,1) == 'low' & catconsumo(:,1)== 'low';
catpreco(mask) = cellfun(@(S) [S, '1'], catpreco(mask), 'Uniform', 0);
mask = catpreco(:,1) == 'medium low' & catconsumo(:,1)== 'medium low';
catpreco(mask) = cellfun(@(S) [S, '2'], catpreco(mask), 'Uniform', 0);
mask = catpreco(:,1) == 'medium' & catconsumo(:,1)== 'medium';
catpreco(mask) = cellfun(@(S) [S, '3'], catpreco(mask), 'Uniform', 0);
mask = catpreco(:,1) == 'medium high' & catconsumo(:,1)== 'medium high';
catpreco(mask) = cellfun(@(S) [S, '4'], catpreco(mask), 'Uniform', 0);
mask = catpreco(:,1) == 'high' & catconsumo(:,1)== 'high';
catpreco(mask) = cellfun(@(S) [S, '5'], catpreco(mask), 'Uniform', 0);

Best Answer

The error message means, that you cannot compare a cell array with a string using the == operator. Use strcmp instead:

cat3    = cell(size(cat1));
cat3(:) = {'0'};
mask       = strcmp(cat1, 'low') & strcmp(cat2, 'low');
cat3(mask) = {'1'};
mask       = strcmp(cat1, 'medium low') & strcmp(cat2, 'medium low');
cat3(mask) = {'2'};
mask       = strcmp(cat1, 'medium') & strcmp(cat2, 'medium');
cat3(mask) = {'3'};
mask       = strcmp(cat1, 'medium high') & strcmp(cat2, 'medium high');
cat3(mask) = {'4'};
mask       = strcmp(cat1, 'high') & strcmp(cat2, 'high');
cat3(mask) = {'5'};

A loop might be nicer:

list = {'low', 'medium low', 'medium', 'medium high', 'high'};
for k = 1:5
  mask       = strcmp(cat1, list{k}) & strcmp(cat2, list{k}));
  cat3(mask) = {sprintf('%d', k)};
end

Related Solutions

MATLAB: How to find subsets of a set or a column

A solution could be ..

 >> data = {'high', 'high', 'high', 'medium', 'low', 'low', 'low', 'medium', ...
            'low', 'medium', 'medium', 'medium', 'high', 'medium'} ;
 >> dataItems = unique(data)
 dataItems = 
    'high'    'low'    'medium'
 >> n = numel(dataItems) ;
 >> combs = arrayfun(@(k)dataItems(combntns(1:n,k)), 1:n, 'UniformOutput', false)
 >> combs{1}                             % Combinations of 1 item.
 ans = 
    'high'    'low'    'medium'
 >> combs{2}                             % Combinations of 2 items.
 ans = 
    'high'    'low'   
    'high'    'medium'
    'low'     'medium'
 >> combs{3}                             % Combination of all items = full set.
 ans = 
    'high'    'low'    'medium'

To understand the internals, look at what we get when we evaluate

 >> ids = arrayfun(@(k)combntns(1:n,k), 1:n, 'UniformOutput', false)
 ids = 
    [3x1 double]    [3x2 double]    [1x3 double]
 >> ids{1}
 ans =
     1
     2
     3
 >> ids{2}
 ans =
     1     2
     1     3
     2     3
 >> ids{3}
 ans =
     1     2     3

so, what we do when we compute combs is to use these ids to index relevant items in dataItems.

Hope it helps!

PS: this is the power set minus the empty set. When you say that you don't want the "power set", do you mean actually that you don't want the set of all elements? If so, you can just replace n by n-1 in the call to ARRAYFUN:

 >> combs = arrayfun(@(k)dataItems(combntns(1:n,k)), 1:n-1, 'UniformOutput', false)
 combs = 
    {1x3 cell}    {3x2 cell}
 >> combs{1}
 ans = 
    'high'    'low'    'medium'
 >> combs{2}
 ans = 
    'high'    'low'   
    'high'    'medium'
    'low'     'medium'

MATLAB: I want to create a new column with words that are atributed regarding the numerical values of another column. How to proceed

It is not possible to put a string into a numeric matrix. You will need to use a table() or a cell array.

NewColumn = repmat( {''}, length(consumption), 1);
mask = consumption >= 3000 & consumption <= 4000;
NewColumn(mask) = cellfun(@(S) [S, 'low'], NewColumn(mask), 'Uniform', 0);
mask = consumption >= 4000 & consumption <= 7000;
NewColumn(mask) = cellfun(@(S) [S, 'medium'], NewColumn(mask), 'Uniform', 0);
mask = consumption >= 7000 & consumption <= 8000;
NewColumn(mask) = cellfun(@(S) [S, 'high'], NewColumn(mask), 'Uniform', 0);

The code would be considerably simpler if your ranges did not overlap -- you have defined 4000 as belonging to both low and medium, and you have defined 7000 as belonging to both medium and high.

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