Column Indexing and help finishing function

Hello,

So for our homework, we are told to finish function "UpdatePriceTable." As shown, I've gotten the basis of the idea but am struggling to figure out how to make the final answer output a 2 x 2 array rather than the 1 x 2 array it is outputting.

I was wondering if: A) I could get a hint for what's wrong B) I could get an extra piece of information to add to make the function the correct answer.

Here's the question;

Column array origPriceTable cotains the price per pound of various deli items. Column array changePrice indicates price adjustments for a given column. Assign newPriceTable with origPriceTable plus the newPriceTable added to origPriceTable's column colNum. Ex: If origPriceTable is [19.99, 9.99; 14.99, 8.99;], changePrice is [ -1.00; -1.50; ], and colNum is 1, then newPriceTable is [18.99, 9.99; 13.49, 8.99;].

And finally here is my current function

function newPriceTable = UpdatePriceTable( origPriceTable, changePrice, colNum )
% UpdatePriceTable: Adds changePrice to column colNum of origPriceTable 
% Returns the updated price table newPriceTable
%   Inputs: origPriceTable - original price data table 
%           changePrice - column array of pricing changes
%           colNum - specified column of priceTable to update
%
%   Outputs: newPriceTable - updated price data table

      % Assign newPriceTable with data from priceTable;
      newPriceTable1 = [origPriceTable(:,colNum) + changePrice]; % FIXME

      % Assign newPriceTable column specified by colNum with original price 
      % data updated by changePrice
      newPriceTable = [newPriceTable(:,:), origPriceTable; % FIXME

end

Thank you for any input or help!

Answer 1

[John Snitzer]

function newPriceTable = UpdatePriceTable( origPriceTable, changePrice, colNum ) % UpdatePriceTable: Adds changePrice to column colNum of origPriceTable % Returns the updated price table newPriceTable % Inputs: origPriceTable - original price data table % changePrice - column array of pricing changes % colNum - specified column of priceTable to update % % Outputs: newPriceTable - updated price data table

    % Assign newPriceTable with data from priceTable;
    newPriceTable = [origPriceTable(:, colNum) + changePrice]; % FIXME

    % Assign newPriceTable column specified by colNum with original price 
    % data updated by changePrice
    origPriceTable(:,colNum) = newPriceTable;
    newPriceTable = origPriceTable(:,:)

end

[Jackson Swets]

good [redacted] bro

Answer 2

[Jos (10584)]

You want to update a single column, but keep the rest! You can do this by indexing on the left hand side of the assignment operator (=), as in

M(:,k) = V % change k-th column of matrix M into the vector V

Note that V should have the same number of elements of as M(:,k), or is a single scalar value, otherwise you'll get the notorious "Dimensions do not match" error.