I have two tables. How can I compare the values in the first column of each table, then do a calculation if the values are equal?

I imported data from two separate files. The data are stored in two separate tables. Each table contains columns of data. The first column is always "pressure." However, sometimes a particular pressure value is missing from one table. For example, Table 1 might be:

Pressure
1
2
3
4
5

while Table 2 is:

Pressure
1
3
4
5
6

I need to find out when the values in each table are the same (i.e., pressures of 1, 3, 4, and 5). Then I need to do a calculation that uses data from those rows and put the results in a third table.

I cannot figure out how to do this. I have tried:

for i=1:length(Table 2)
    if Table1(i) == Table2(i)
        Table3.append(Table1 .* 0.05) + (Table2 .* 0.95);
    end
end

However, I get the error:

Arrays have incompatible sizes for this operation.

I would be grateful for any advice. Thank you.

Answer 1

[Hassaan]

@Srh Fwl A basic idea.

% Example initialization with an additional data column
Table1 = table([1; 2; 3; 4; 5], rand(5, 1), 'VariableNames', {'Pressure', 'DataColumn'});
Table2 = table([1; 3; 4; 5; 6], rand(5, 1), 'VariableNames', {'Pressure', 'DataColumn'});

% Find common 'Pressure' values
commonPressures = intersect(Table1.Pressure, Table2.Pressure);

% Initialize Table3 to store results
Table3 = table([], [], 'VariableNames', {'Pressure', 'Result'});

for i = 1:length(commonPressures)
    % Find rows in each table that match the current pressure
    rowInTable1 = Table1.Pressure == commonPressures(i);
    rowInTable2 = Table2.Pressure == commonPressures(i);
    
    % Use logical indexing to access the 'DataColumn' for calculations
    result = (Table1.DataColumn(rowInTable1) * 0.05) + (Table2.DataColumn(rowInTable2) * 0.95);
    
    % Append the common pressure and result to Table3
    Table3 = [Table3; {commonPressures(i), result}];
end

% Display the result
disp(Table3);

    Pressure    Result 
    ________    _______

       1        0.43724
       3          0.558
       4         0.4823
       5        0.75785

DataColumn Added: The example assumes an additional column named 'DataColumn' exists in both tables for the calculation.

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[Siddharth Bhutiya]

You could actually simplify this code. You can use the second and third output of intersect to get the rows from both the tables that correspond to the commonPressures. Using that you can vectorize your result calculation and directly use that to create the results table.

% Example initialization with an additional data column
Table1 = table([1; 2; 3; 4; 5], rand(5, 1), VariableNames=["Pressure", "DataColumn"]);
Table2 = table([1; 3; 4; 5; 6], rand(5, 1), VariableNames=["Pressure", "DataColumn"]);
% Find common 'Pressure' values
[commonPressures, rowInTable1, rowInTable2] = intersect(Table1.Pressure, Table2.Pressure);
% Compute the results
result = (Table1.DataColumn(rowInTable1) * 0.05) + (Table2.DataColumn(rowInTable2) * 0.95);
% Put these values into a table
Table3 = table(commonPressures, result, VariableNames=["Pressure", "DataColumn"])

Table3 = 4×2 table
    Pressure    DataColumn
    ________    __________

       1         0.70896  
       3         0.51712  
       4          0.5561  
       5         0.69906  

[Srh Fwl]

Thank you very much, Siddharth. I will try this out.

[Hassaan]

You are welcome