convert categorical column to numeric in a matrix?

I have a matrix 147*26.I attached that here.some column are categorical data and I want convert them to numeric.what should I do? thanks for help

Answer 1

[Yuvaraj Venkataswamy]

Try this FAQ.

https://in.mathworks.com/matlabcentral/answers/264383-convert-categorical-to-numeric

[z donyavi]

when I import tra2 in matlab it's imported as a cell array. For example I want convert column 3 of tra2 to numeric.

   tra2(:,3)=grp2idx(categorical(tra2(:,3)))
Conversion to cell from double is not possible.

[dpb]

Well, that's entirely different than being categorical.

[Yuvaraj Venkataswamy]

From double to cell conversion you can use num2cell()

Answer 2

[dpb]

>> Stations = {'S1';'S2';'S1';'S3';'S2'};
Stations = categorical(Stations)
Stations = 
  5×1 categorical array
     S1 
     S2 
     S1 
     S3 
     S2 
>> double(Stations)
ans =
     1
     2
     1
     3
     2
>>

Answer 3

[dpb]

Totally different Q? in follow up than original --

You don't show how you "imported" the file, but

 >> [~,~,r]=xlsread('tra2.xls');
 >> cell2mat(r(2:10,2))
ans =
     3
     1
    14
    13
     1
     9
     5
    17
     1
>>

From the raw cell array have to skip the header row to convert, hence the (2) as starting index.

Alternatively, and much easier to deal with in the end would be--

>> t=readtable('tra2.xls');
Warning: Variable names were modified to make them valid MATLAB identifiers. The original names are saved in the VariableDescriptions property. 
>> t(1:10,:)
ans =
  10×26 table
    Normalized_losses    Make    Fuel_type    Aspiration    Num_of_doors    Body_style     Drive_wheels    Engine_location    Wheel_base    Length    Width    Height    Curb_weight    Engine_type    Num_of_cylinders    Engine_size    Fuel_system    Bore    Stroke    Compression_ratio    Horsepower    Peak_rpm    City_mpg    Highway_mpg    Price    Symboling
    _________________    ____    _________    __________    ____________    ___________    ____________    _______________    __________    ______    _____    ______    ___________    ___________    ________________    ___________    ___________    ____    ______    _________________    __________    ________    ________    ___________    _____    _________
    110                   3      'gas'        'std'         'four'          'sedan'        'fwd'           'front'            96.5          163.4       64     54.5      2010           'ohc'          'four'               92            '1bbl'         2.91    3.41       9.2                  76           6000        30          34              7295    '0'      
    134                   1      'gas'        'std'         'two'           'hatchback'    'rwd'           'front'            98.4          176.2     65.6       52      2551           'ohc'          'four'              146            'mpfi'         3.62     3.5       9.3                 116           4800        24          30              9989    '2'      
    125                  14      'gas'        'std'         'four'          'sedan'        'fwd'           'front'            96.3          172.4     65.4     51.6      2405           'ohc'          'four'              122            '2bbl'         3.35    3.46       8.5                  88           5000        25          32              8189    '1'      
    104                  13      'gas'        'turbo'       'four'          'sedan'        'fwd'           'front'            99.1          186.6     66.5     56.1      2847           'dohc'         'four'              121            'mpfi'         3.54    3.07         9                 160           5500        19          26             18620    '2'      
     91                   1      'gas'        'std'         'four'          'sedan'        'fwd'           'front'            95.7          166.3     64.4     52.8      2140           'ohc'          'four'               98            '2bbl'         3.19    3.03         9                  70           4800        28          34              9258    '0'      
    115                   9      'gas'        'std'         'four'          'hatchback'    'fwd'           'front'            98.8          177.8     66.5     55.5      2425           'ohc'          'four'              122            '2bbl'         3.39    3.39       8.6                  84           4800        26          32             11245    '0'      
    122                   5      'gas'        'std'         'four'          'sedan'        'fwd'           'front'            94.5          165.3     63.8     54.5      1938           'ohc'          'four'               97            '2bbl'         3.15    3.29       9.4                  69           5200        31          37              6849    '1'      
    121                  17      'gas'        'std'         'two'           'hatchback'    'fwd'           'front'            88.4          141.1     60.3     53.2      1488           'l'            'three'              61            '2bbl'         2.91    3.03       9.5                  48           5100        47          53              5151    '2'      
    134                   1      'gas'        'std'         'two'           'hardtop'      'rwd'           'front'            98.4          176.2     65.6       52      2540           'ohc'          'four'              146            'mpfi'         3.62     3.5       9.3                 116           4800        24          30              8449    '2'      
     93                  15      'diesel'     'turbo'       'four'          'wagon'        'rwd'           'front'             110          190.9     70.3     58.7      3750           'ohc'          'five'              183            'idi'          3.58    3.64      21.5                 123           4350        22          25             28248    '-1'     
>>

>> t.Make(1:10)
ans =
     3
     1
    14
    13
     1
     9
     5
    17
     1
    15
>>

and Make will be double by default. I'd suggest converting it to categorical would probably be beneficial, though instead of numeric.

[z donyavi]

sorry I'm so confused.I want convert categorical column of 'tra2' to numeric.

[dpb]

You've got us totally confused by not showing what you've done...we have to try to guess what the starting point is.

Show the code you used to import the data into Matlab and what does

whos tra2

show so we can tell what it is we're trying to work with. Or, attach tra2.mat to provide us the same data precisely as you have.

But, whatever you did, why not convert to using table from the spreadsheet and you'll have the numeric data in numeric form automagically.

[z donyavi]

I use this command for import data

[~,~,raw] = xlsread('tra2.xls')

[dpb]

Well, that was the first response I showed you...I just did a few elements instead of the whole column. Replace (2:10,2) with (2:end,2). Again note you must manually avoid trying to do something you can't with the header row this way and will have to continue to do that every time you try to access anything.

If you were to forget about xlsread and the cell array in favor of readtable and a table you'll get along a lot faster going forward.

And, that kind of a variable really ought to be categorical, not numeric, as should a significant number of the others.

A subset of the first 10 lines, first six variable...of those four should be categorical assuming the losses are actually a measured or calculated response. and one that is categorical would make a lot of sense as being numerical altho if it is only for classification as is quite probable it could well be left as categorical, too...

>> t(1:10,1:6)
ans =
  10×6 table
    Normalized_losses    Make    Fuel_type    Aspiration    Num_of_doors    Body_style 
    _________________    ____    _________    __________    ____________    ___________
    110                   3      'gas'        'std'         'four'          'sedan'    
    134                   1      'gas'        'std'         'two'           'hatchback'
    125                  14      'gas'        'std'         'four'          'sedan'    
    104                  13      'gas'        'turbo'       'four'          'sedan'    
     91                   1      'gas'        'std'         'four'          'sedan'    
    115                   9      'gas'        'std'         'four'          'hatchback'
    122                   5      'gas'        'std'         'four'          'sedan'    
    121                  17      'gas'        'std'         'two'           'hatchback'
    134                   1      'gas'        'std'         'two'           'hardtop'  
     93                  15      'diesel'     'turbo'       'four'          'wagon'    
>>