MATLAB: Use values in double array to determine values in a cell array of strings

Question

I have a 597x4 double array that constitutes student marks in a subject. Each value in that array is between 0 and 100.

I want to create an 597x4 cell array of strings, where each cell contains a string connected to the equivalent location in the double array.

Everyone who scored 80 or more gets an 'A'. Therefore, if (1,1) of the double array contains 84 then (1,1) of the cell array should be 'A'. Let's say the breakdown is > 80 = 'A', < 80 but > 50 = 'B', and otherwise 'C'.

I realise this could easily be done with a loop, but is there a more elegant way? This is in MATLAB, but ultimately I want to paste the values into an Excel file.

I edited the post to clarify the grading structure a bit more. — user1205901 - Слава Україні
– user1205901 - Слава Україні, Commented Nov 22, 2015 at 13:52

Divakar · Accepted Answer · 2015-11-22 14:46:58Z

2

Here's one with bsxfun and some reshaping -

factions = [0,30,50,80] %// Edit this if you want more factions
remarks = {'Doomed','Fail','Good','Very good'}; %// Editable too

rank = sum(bsxfun(@ge,arr,permute(factions,[1 3 2])),3);
out = reshape(cellstr(char(max(rank(:))-rank(:)+'A')),size(arr))
out_remarks = remarks(rank)

Sample input, output -

arr =
     3    81    73    38    88
    56    90    58    94    94
    31    60     3    83    67
    94    89    45    85    21
    99    95    65    38    66
    29    55    53    60     8
factions =
     0    30    50    80
out = 
    'D'    'A'    'B'    'C'    'A'
    'B'    'A'    'B'    'A'    'A'
    'C'    'B'    'D'    'A'    'B'
    'A'    'A'    'C'    'A'    'D'
    'A'    'A'    'B'    'C'    'B'
    'D'    'B'    'B'    'B'    'D'
out_remarks = 
    'Doomed'       'Very good'    'Good'      'Fail'         'Very good'
    'Good'         'Very good'    'Good'      'Very good'    'Very good'
    'Fail'         'Good'         'Doomed'    'Very good'    'Good'     
    'Very good'    'Very good'    'Fail'      'Very good'    'Doomed'   
    'Very good'    'Very good'    'Good'      'Fail'         'Good'     
    'Doomed'       'Good'         'Good'      'Good'         'Doomed'

edited Nov 22, 2015 at 14:46

answered Nov 22, 2015 at 14:05

Divakar

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3 Comments

user1205901 - Слава Україні Over a year ago

This is brilliant! I particularly like how the factions can be altered flexibly. Would I need to also change the final '3' in rank = sum(bsxfun(@ge,arr,permute(factions,[1 3 2])),3); if I added more factions?

Divakar Over a year ago

@user1205901 Nope, just edit the factions array, rest of the code takes care of everything!

user1205901 - Слава Україні Over a year ago

Cool, and sorry to bother with another question, but if one day I wanted to change the actual grades (e.g. change 'A' to 'Very good', 'B' to 'Good', and 'C' to 'Fail'), can I simply edit out = reshape(cellstr(char(max(rank(:))-rank(:)+'A')),size(arr))? Or would I need to take different approach?

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