If Statement Using Text in a Table

What commands can I use in the following if statement to specify blank element overwrite?

% Run throught the table of 10 rows
for i = 1:10

    % The word "REMOVE" has been used in a previous condition subroutine to specify the row removal in this if statment
 if strcmp("REMOVE",table1(i,1)) == 1

    % Emptys rows
table1(i,:) = []

else

end

end

The subroutine is executed and the table rows are not being emptied when true

Answer 1

[madhan ravi]

I have no idea why you need a loop ( https://in.mathworks.com/help/matlab/matlab_prog/access-data-in-a-table.html ):

T=table({'asdsa';'REMOVE'}); % example
idx=strcmp(T{:,1},"REMOVE");
T(idx,:) = [] % remove those rows

[Jay]

Thank you Madhan.

Can you please tell me why you have specified 'asdsa' and what it does in your code?

[Jay]

I get the following error returned:

Subscripting a table using linear indexing (one subscript) or multidimensionalindexing (three or more subscripts) is not supported. Use a row subscript and a variable subscript.

[madhan ravi]

It was just an example. Show the code that your using. Which version of MATLAB are you using? Upload your table as .mat file. Also determine which variable of the table you want to work on.

[Jay]

clear
clc

%% INPUT
arr_1 = cell(10,4)

% Names
stringVals = {"Test 1", "Test 2", "REMOVE", "Test 4", "Test 5"}'

% Populate names
arr_1 = repmat(stringVals(1:5,1),2,1)

% Populate columns 2:4 with rand
for i =2:4
    
    for j = 1:size(arr_1(:,1))
        
    arr_1(j,i) = num2cell(randn)
    
    end
    
end

% Convert to table
arr_1 = cell2table(arr_1)

%% Madhan's Code


T=arr_1({'REMOVE'}); % example
idx=strcmp(arr_1{:,1},"REMOVE");
arr_1(idx,:) = [] % remove those rows

[Walter Roberson]

T=arr_1({'REMOVE'}, :);

[madhan ravi]

So doesn’t the below lines do what you want??

idx=strcmp(arr_1{:,1},"REMOVE");
arr_1(idx,:) = [] % remove those rows

[Jay]

I get the following error is thrown when executing:

T=arr_1({'REMOVE'},:); % example

Unrecognized row name 'REMOVE'.

The code as it stands is (in case I am missing something):

clear

clc


%% INPUT
arr_1 = cell(10,4)

% Names
stringVals = {"Test 1", "Test 2", "REMOVE", "Test 4", "Test 5"}'

% Populate names
arr_1 = repmat(stringVals(1:5,1),2,1)

% Populate columns 2:4 with rand
for i =2:4
    
    for j = 1:size(arr_1(:,1))
        
    arr_1(j,i) = num2cell(randn)
    
    end
    
end

% Convert to table
arr_1 = cell2table(arr_1)


%% Madhan's Code

T=arr_1({'REMOVE'},:); % example
idx=strcmp(arr_1{:,1},"REMOVE");
arr_1(idx,:) = [] % remove those rows

The code does not remove the "REMOVE" rows.

[Stephen23]

"I get the following error ...Unrecognized row name 'REMOVE'."

Get rid of the T=... line.

Using loops like that to generate the table is very complex and inefficient. Simpler:

>> T = array2table(randn(10,3),'VariableNames',{'A','B','C'});
>> T.names = repmat({'Test 1';'Test 2';'REMOVE';'Test 4';'Test 5'},2,1)
T = 
        A           B           C         names  
    _________    ________    ________    ________
     -0.62909     -1.3981     0.88095    'Test 1'
      -1.2038    -0.25506     0.32321    'Test 2'
     -0.25394      0.1644    -0.78415    'REMOVE'
      -1.4286     0.74773     -1.8054    'Test 4'
    -0.020858    -0.27305      1.8586    'Test 5'
     -0.56066      1.5763    -0.60453    'Test 1'
       2.1778    -0.48094     0.10336    'Test 2'
       1.1385     0.32751     0.56317    'REMOVE'
      -2.4969     0.66473      0.1136    'Test 4'
      0.44133    0.085189    -0.90473    'Test 5'
>> X = strcmp(T.names,'REMOVE');
>> T(X,:) = [] % remove those rows
T = 
        A           B           C         names  
    _________    ________    ________    ________
     -0.62909     -1.3981     0.88095    'Test 1'
      -1.2038    -0.25506     0.32321    'Test 2'
      -1.4286     0.74773     -1.8054    'Test 4'
    -0.020858    -0.27305      1.8586    'Test 5'
     -0.56066      1.5763    -0.60453    'Test 1'
       2.1778    -0.48094     0.10336    'Test 2'
      -2.4969     0.66473      0.1136    'Test 4'
      0.44133    0.085189    -0.90473    'Test 5'

See also:

https://www.mathworks.com/help/matlab/matlab_prog/access-data-in-a-table.html

[Jay]

I found an older answer deleting all rows from a table that contain a string you wrote madhan which fixed the problem.

Command used is now :

arr_1(~any(strcmp(arr_1{:,:},"REMOVE"),2),:)

I wish I came across it sooner.

Thank you for your help.

[Guillaume]

With the example you provide,

idx=strcmp(arr_1{:,1},"REMOVE");
arr_1(idx,:) = [] % remove those rows

does remove the unwanted rows and I can't see why it wouldn't do so for you. This syntax has always been valid for tables.

On the other hand, since you're using strings and not char vectors, you can use simply:

toremove = arr_1{:, 1} == "REMOVE";
arr_1(toremove, :) = []

This is equivalent to Madhan's code.

As Madhan said, there's usually no reason to use loops with tables. The way you construct your demo table is very inefficient. You could have done:

stringVals = {"Test 1", "Test 2", "REMOVE", "Test 4", "Test 5"}';
arr_1 = cell2table([repmat(stringVals, 2, 1), num2cell(randn(2*numel(stringVals), 3))])

[Jay]

Hi Stephen,

The code listed is to demonstrate what I am trying to achieve for a section of a reduction program.

For the purpose of the program I am writing, the names in the first column will differ and having to "hard code" the values would be to inefficient in the larger scheme of things (and potentially lead to more errors).

My exposure to MATLAB (at university) has been using if and for statements and reading in an excel spreadsheet.

I am coding to streamline the reductions required for another unit.

I have only been introduced to tables and cells (along with their syntax requirements for a week or so) so still learning.

Guillaume,

You are correct, but only when the

%T=arr_1({'REMOVE'},:); % example

has been removed from the code.

I only found that out when you stated that the code works and commented out the first of 3 additional commands (under the "% Madhan's Code).

Thank you for your time and effort Walter, Stephan and Guillaume.

[Walter Roberson]

T=arr_1({'REMOVE'}, :);

is for the case where you have specified a RowNames property for the table, which you have not done so. Without a RowNames property, the {'REMOVE'} indexing would not know which of the table fields to match against.

[Jay]

Thank you for explaining what that command does Walter.

The explanations by the more advanced contributors help a lot more in understanding commands that exceed the simpler commands in the Matlab documentation.

[Walter Roberson]

https://www.mathworks.com/help/matlab/matlab_prog/limitations-of-tables-and-timetables.html