For Loop Question on index

I have an example data:

Column 1 is Student Number, Column 2-4 are grades

1.0 68.0 45.0 92.0

2.0 83.0 54.0 93.0

3.0 61.0 67.0 91.0

4.0 70.0 66.0 92.0

5.0 75.0 68.0 96.0

6.0 82.0 67.0 90.0

How can I create a for loop that would sum Column 2-4 and relate it back to the student number.

It should print out: "Student" 1 "Total_score" 205 (This added columns 2-4)"

Thanks!

[James Tursa]

What have you done so far? What specific problems are you having with your code? Are you required to use a for-loop?

Answer 1

[Voss]

data = [ ...
    1.0  68.0  45.0  92.0; ...
    2.0  83.0  54.0  93.0; ...
    3.0  61.0  67.0  91.0; ...
    4.0  70.0  66.0  92.0; ...
    5.0  75.0  68.0  96.0; ...
    6.0  82.0  67.0  90.0; ...
    ];

total = sum(data(:,2:4),2);

for i = 1:size(data,1)
    fprintf('"Student" %d  "Total_score" %g (This added columns 2-4)"\n',data(i,1),total(i,1));
end

"Student" 1  "Total_score" 205 (This added columns 2-4)"
"Student" 2  "Total_score" 230 (This added columns 2-4)"
"Student" 3  "Total_score" 219 (This added columns 2-4)"
"Student" 4  "Total_score" 228 (This added columns 2-4)"
"Student" 5  "Total_score" 239 (This added columns 2-4)"
"Student" 6  "Total_score" 239 (This added columns 2-4)"

Or, if you really want to do the sum in a loop:

total = NaN(size(data,1),1);
for i = 1:size(data,1)
    total(i) = data(i,2)+data(i,3)+data(i,4);
end

for i = 1:size(data,1)
    fprintf('"Student" %d  "Total_score" %g (This added columns 2-4)"\n',data(i,1),total(i,1));
end

"Student" 1  "Total_score" 205 (This added columns 2-4)"
"Student" 2  "Total_score" 230 (This added columns 2-4)"
"Student" 3  "Total_score" 219 (This added columns 2-4)"
"Student" 4  "Total_score" 228 (This added columns 2-4)"
"Student" 5  "Total_score" 239 (This added columns 2-4)"
"Student" 6  "Total_score" 239 (This added columns 2-4)"

[James Tursa]

Homework is getting easier all the time ...

[Michael Angeles]

Could you explain the second 2 on: total = sum(data(:,2:4),2);

Thanks!!

[Voss]

The second 2 is to tell the sum() function to sum along the 2nd dimension. See the description in the documentation here.

[Michael Angeles]

Thank you!