How to replace elements of a cell array using a containers.Map

Question

Bill Tubbs 2021-1-19

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https://ww2.mathworks.cn/matlabcentral/answers/721449-how-to-replace-elements-of-a-cell-array-using-a-containers-map

评论： Bill Tubbs 2021-2-1

I have a cell array of VariableNames that Matlab created when reading a csv file. I want to change them to my own choice of names however, the order of the names is not guaranteed.

iddata = readtable('data.csv');
var_names = iddata.Properties.VariableNames;
names_to_replace = {'TonnageDeBSA', 'D__bitD___eauAuBSA', ...
                    'PressionPalierSAG', 'PuissanceSAG'};
replacements = {'TonnageBSA', 'DebitEauBSA', ...
                'PressionPalierSAG', 'PuissanceSAG'};
replace_map = containers.Map(names_to_replace, replacements);

Obviously I could use a for loop:

new_var_names = {};
for i=1:numel(var_names)
    new_var_names(i) = {replace_map(var_names{i})};
end

But I am hoping there is an easier way.

Does MATLAB have anything like a list comprehension in Python?

new_var_names = {replace_map[name] for name in var_names}

Even better if there is a way to handle failed matches:

new_var_names = {replace_map[name] for name in var_names if name in replace_map}

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Answer 1

Puru Kathuria 2021-1-31

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https://ww2.mathworks.cn/matlabcentral/answers/721449-how-to-replace-elements-of-a-cell-array-using-a-containers-map#answer_610858

You might want to try out arrayfun, which can help you in applying a function to each element of array.

Otherwise, you can also do the above mentioned operation traditionally using for loop.

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Bill Tubbs 2021-1-31

在 MATLAB Online 中打开

I couldn't get arrayfun to work but cellfun does.

Is this what you meant?

new_var_names = cellfun(@(s) replace_map(s), var_names, 'UniformOutput', false)

per isakson 2021-2-1

编辑：per isakson 2021-2-1

Most likely, yes. Had the texts been stored in string arrays then arrayfun had done the job.

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Answer 2

per isakson 2021-2-1

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https://ww2.mathworks.cn/matlabcentral/answers/721449-how-to-replace-elements-of-a-cell-array-using-a-containers-map#answer_611918

在 MATLAB Online 中打开

With string and arrayfun on R2018b

%%
names_to_replace = ["TonnageDeBSA", "D__bitD___eauAuBSA", ...
                    "PressionPalierSAG", "PuissanceSAG"];
replacements = ["TonnageBSA", "DebitEauBSA", ...
                "PressionPalierSAG", "PuissanceSAG"];
            
replace_map = containers.Map( names_to_replace, replacements );
%%
var_names = names_to_replace( randi([1,4],1,8) );  % test data 
new_names = arrayfun( @(key) replace_map(key), var_names, "uni", false );
reshape( new_names, [],1 )

outputs

ans =
  8×1 cell array
    {'PuissanceSAG'     }
    {'DebitEauBSA'      }
    {'PressionPalierSAG'}
    {'TonnageBSA'       }
    {'PuissanceSAG'     }
    {'DebitEauBSA'      }
    {'PressionPalierSAG'}
    {'PressionPalierSAG'}
>> 

Surprise, I expected a string array as output. containers.Map (R2018b) doesn't seem to fully support strings.

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Bill Tubbs 2021-2-1

Thanks, but the original source of the names is a cell array (from table.Properties.VariableNames) so I think cellfun is the best option as per my comment on the other answer.

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