How to find the last column index in excel with Matlab

Question

I am writing data as matrices into excel file using Matlab. My matrices\' dimension varies and I don\'t know the matrices\' dimension in advance. Let\'s say I have matrix A,

Answer 1

To calculate an Excel column ID based on an index number I made the following function:

function col = excel_column(n)

    %// find LSB
    xlsb = mod(n-1,26)+1 ;
    xmsb = fix((n-1)/26) ;

    %// find MSB (recursively if necessary)
    if xmsb >= 1
        col = [excel_column(xmsb) char(xlsb+64)] ;
    else
        col = char(xlsb+64) ;
    end

This will work for any number, but be careful that Excel has a maximum number of column (2^14=16384 columns max in my version). As an example, to shows that it handles the letter incrementation, you can run the short test:

>> x = [25:28 233:236 700:705 16383:16385] ;
for n=x
    fprintf('Index: %5d => Column: %s\n', n , excel_column(n) )
end

Index:    25 => Column: Y
Index:    26 => Column: Z
Index:    27 => Column: AA
Index:    28 => Column: AB
Index:   233 => Column: HY
Index:   234 => Column: HZ
Index:   235 => Column: IA
Index:   236 => Column: IB
Index:   700 => Column: ZX
Index:   701 => Column: ZY
Index:   702 => Column: ZZ
Index:   703 => Column: AAA
Index:   704 => Column: AAB
Index:   705 => Column: AAC
Index: 16383 => Column: XFC
Index: 16384 => Column: XFD %// Last real column
Index: 16385 => Column: XFE %// Careful. This column DOES NOT exist in Excel

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So in your case, You start to write your matrix A at column 'B...', which is column index 2. To know where to start your matrix B, simply calculate the size of A and add the necessary gap. Let's say your matrix A has 573 columns.

startIdx_A   = 2 ;         %// Matrix "A" started at column index 2
ncA          = size(A,2) ; %// Number of column in A, should return 573
columnGap    = 1 ;         %// how much gap you want between "A" and "B"

startColumnMatrixB_index = startIdx + ncA + columnGap ; %// index of the first column for Matrix "B"
startColumnMatrixB_excel = excel_column(startColumnMatrixB_index) ; %// return 'VD' (assuming A had 573 columns)

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If your matrices are very large (in number of columns), it would be prudent to include a check to make sure you won't run out of column before you call the xlswrite