Loren on the Art of MATLAB

Turn ideas into MATLAB

Dealing with Cells 37

Posted by Loren Shure,

A customer recently asked me this question at the MATLAB Virtual Conference.

Contents

Question about Summing Cell Rows

  I was hoping you would cover cells some day. Here is a particular
  problem I was hoping to have a more elegant solutions for.
  A is a cell that has String (say names) in the first column, Numbers
  (say scores in tests 1 and 2) in the next two columns. Assume that each
  cell has only one value. Is there an easier way to calculate, say the
  sum of the two test scores than a for loop?

Example

Let's make some sample data.

c(1:4,1) = {'Fred' 'Alice' 'Lucy' 'Tom'};
c(1:4,2) = { 90  80  55 102 };
c(1:4,3) = { 43  91  80  44 }
c = 
    'Fred'     [ 90]    [43]
    'Alice'    [ 80]    [91]
    'Lucy'     [ 55]    [80]
    'Tom'      [102]    [44]

Answer

To sum the entries in a row for this cell array, I can simply turn the numeric values into a numeric array via comma-separated list notation, and then sum the rows. Let's see the pieces for clarity. Here's the comma-separated list.

c{:,2:3}
ans =
    90
ans =
    80
ans =
    55
ans =
   102
ans =
    43
ans =
    91
ans =
    80
ans =
    44

Now place the results into a vector.

vec = [c{:,2:3}]
vec =
    90    80    55   102    43    91    80    44

Reshape the vector appropriately into a matrix.

array = reshape(vec,[],2)
array =
    90    43
    80    91
    55    80
   102    44

Now sum the results along the rows.

tot = sum(array,2)
tot =
   133
   171
   135
   146

Or, in one bigger statement, try this.

tot = sum(reshape([c{:,2:3}],[],2),2)
tot =
   133
   171
   135
   146

Cell Array Questions

Do you use cell arrays? Can you do what you want without undo contortions? Let me know here.


Get the MATLAB code

Published with MATLAB® 7.9

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