如何将矩阵中的列乘以不同的常数（每列），然后在Matlab中将每一行求和？

Question

For a project, I have a set amount of orders coming in and I am trying to calculate the total for each total. After multiplying each column (number of each item) of the matrix by a set constant (each price pertains to a different column in the matrix), I would like to sum all the cells in each row so that I can find the total price per each order. This is the code I have so far:

%A is the matrix of item types and quantities of each item

%A = |OrderNumber  Kitkat   Hershey   Reese's .....  Rolo|
     |  1            3        4        2      .....   4  |
     |  2            4        10       9      .....   2  |
     |  3            7        8        0      .....   0  |
     |.....         ....     ...      ...     ..... .....|

candyPrice = [3 4 3 ........];
orderTotalPrice = {}; 
for i = 1:10
  for k = 2:10
    orderTotalPrice(i) = A(i,k).*candyPrice(k)+orderTotalPrice;        
end
end

I am getting error messages when I run this code, saying that "Undefined function 'plus' for input arguments of type 'cell'."

Answer 1

For the question title:

" multiply columns in a matrix by a different constant (per column) and then summing each row up in Matlab? "

one symbol, * will do this, (as mentioned in comments as vector-matrix product)

What you are trying to calculate is equivalent to

orderTotalPrice = candyPrice*matA

where candyPrice is a 1xn vector and matA is nxm (n being the number of item types and m being the number of orders...)

For OP's code

To use this method with the cell A we need to

• Remove the order numbers and titles
• Convert from cell to matrix
• Transpose (to be numitemtypes x numorders)

So the one-liner which performs all this is:

orderTotalPrice = candyPrice*cell2mat(A(2:end,2:end)).'

with the test data

A = 

    'orderNo'    'item1'    'item2'    'item3'
    [      1]    [    2]    [    1]    [    3]
    [      2]    [    3]    [    2]    [    3]
    [      3]    [    1]    [    3]    [    3]


candyPrice =

   100    10     1

we get

orderTotalPrice = candyPrice*cell2mat(A(2:end,2:end)).'

orderTotalPrice =

   213   323   133

Answer 2

Use p1 = bsxfun(@times,A(:,2:end),candyPrice) to compute the prices of all products. The total order price for each candy is p2 = sum(p1,2) and the total price is p = sum(p2) .

---

Alternatively, you adjust your code like this:

candyPrice = [3 4 3 ........];
orderTotalPrice = zeros(1,10);
for i = 1:10
    for k = 2:10
        orderTotalPrice(i) = A(i,k).*candyPrice(k)+orderTotalPrice(i);
    end
end
total = sum(orderTotalPrice);

Answer 3

First of all, the orderNumber should not be multiplied with anything, otherwise it won't make any sense.

Therefore, I assume that size(candyPrice,2) equals size(A,2)-1

Then the vectorized code would be as follows:

orderTotalPrice = sum(repmat(candyPrice,[size(A,1) 1]).*A(:,2:end),2);