Box plot for column of a table with categorical variables

I have a table of different varieties of apples and their prices.

I'm trying to create a box plot for each variety, with the variety names as the categorical variables and show them on the same chart.

Here's my attempt:

T=readtable('fruitvegprices2.csv');
items={'apples','pears','carrots','cabbage'};

%apples
[idx,ia] = ismember(T.(2),items{1});
T_apples = T(idx,{'item','variety'});% this gives table of apples alone 
S_apples=unique(T_apples,'stable') %distinct varieties of apples


A=sortrows(T(idx,{'item','variety','price'})) %grouping the varieties together

var_order=S_apples.variety;
namedvar=categorical(A.price,1:8,var_order);

plot=boxchart(namedvar,A.price)
xlabel('Variety')
ylabel('Price')

The output I get is:

I don't know how to fix this, also I can't seem to turn off the Latex interpreter for the x-axis labels.

Could I get some help please?

Thank you!

[Walter Roberson]

A=sortrows(T(idx,{'item','variety','price'})) %grouping the varieties together

sortrows() sorts first by the first column, which in this case would be 'item', not 'variety' ?

But you already know that T(idx,:) is only for apples, so it is not clear why you bother extracting and sorting on the item field, since the field should be the same for everything in the subset ?

[Cris LaPierre]

Share your data file. You can attach it using the paperclip icon.

[Achuan Chen]

Sorry, I've now attached the Excel file.

[Achuan Chen]

Yes that was unnecessary, I've now ammended this line to

A=sortrows(T(idx,{'variety','price'}))

since all entries in 'item' are apples.

[Achuan Chen]

Update:

I've created a cell C, where column i of C = prices of variety i = i-th entry of S_apples.variety, so all I need to do now is to make a boxplot of C, and in theorey it will make a box plot for each column of C, and C has 8 columns for the 8 distinct varieties:

T=readtable('fruitvegprices.csv');

Error using readtable (line 498)
Unable to find or open 'fruitvegprices2.csv'. Check the path and filename or file permissions.

items={'apples','pears','carrots','cabbage'};

%apples
[idx,ia] = ismember(T.(2),items{1});
T_apples = T(idx,{'item','variety'});% this gives table of apples alone 
S_apples=unique(T_apples,'stable') %distinct varieties of apples

A=sortrows(T(idx,{'variety','price'})) %grouping the varieties together

C=cell(length(S_apples.variety),1);%column i=prices of variety i
for i=1:length(S_apples.variety)
    [c,d]=ismember(A.variety,S_apples.(2){i});
    
    for k=1:length(A(c,:).price)
        C{k,i}=A(c,:).price(k);
    end
    
end
C(find(cellfun(@isempty,C)))={nan};
boxchart(C)

However, it comes up with the message:

;

all the cell entries are integers so I don't see why there's a problem, and I've assigned NaN to the empty cells so this should work. What's gone wrong?

Thank you!

[Walter Roberson]

@Achuan Chen

Are you sure you want your posts to be considered Spam ? That could result in Mathworks closing your account.

Answer 1

[Cris LaPierre]

Not sure what your solution was, but this is how I would create the boxchart

% Load data
opts = detectImportOptions('fruitvegprices.csv');
opts = setvartype(opts,["category","item","variety","unit"],"categorical");
data = readtable('fruitvegprices.csv',opts)

data = 9148×6 table
    category           item               variety             date       price    unit
    _________    ________________    __________________    __________    _____    ____

    fruit        apples              bramleys_seedling     2021-11-12    1.49     kg  
    fruit        apples              coxs_orange_group     2021-11-12    1.09     kg  
    fruit        apples              egremont_russet       2021-11-12    1.14     kg  
    fruit        apples              braeburn              2021-11-12    1.01     kg  
    fruit        apples              gala                  2021-11-12    1.01     kg  
    fruit        apples              other_early_season    2021-11-12    0.95     kg  
    fruit        pears               conference            2021-11-12    1.04     kg  
    fruit        pears               doyenne_du_comice     2021-11-12    1.08     kg  
    fruit        raspberries         raspberries           2021-11-12     4.4     kg  
    fruit        strawberries        strawberries          2021-11-12    6.24     kg  
    vegetable    beetroot            beetroot              2021-11-12    0.51     kg  
    vegetable    brussels_sprouts    brussels_sprouts      2021-11-12    0.98     kg  
    vegetable    pak_choi            pak_choi              2021-11-12    2.72     kg  
    vegetable    curly_kale          curly_kale            2021-11-12    3.26     kg  
    vegetable    cabbage             red                   2021-11-12    0.55     kg  
    vegetable    cabbage             savoy                 2021-11-12     0.5     head

% create table of just the apples
apples = data(data.item=="apples",:)

apples = 985×6 table
    category     item          variety             date       price    unit
    ________    ______    __________________    __________    _____    ____

     fruit      apples    bramleys_seedling     2021-11-12    1.49      kg 
     fruit      apples    coxs_orange_group     2021-11-12    1.09      kg 
     fruit      apples    egremont_russet       2021-11-12    1.14      kg 
     fruit      apples    braeburn              2021-11-12    1.01      kg 
     fruit      apples    gala                  2021-11-12    1.01      kg 
     fruit      apples    other_early_season    2021-11-12    0.95      kg 
     fruit      apples    bramleys_seedling     2021-11-05    1.56      kg 
     fruit      apples    coxs_orange_group     2021-11-05    1.09      kg 
     fruit      apples    egremont_russet       2021-11-05    1.18      kg 
     fruit      apples    braeburn              2021-11-05     1.2      kg 
     fruit      apples    gala                  2021-11-05       1      kg 
     fruit      apples    other_early_season    2021-11-05    0.95      kg 
     fruit      apples    bramleys_seedling     2021-10-29    1.51      kg 
     fruit      apples    coxs_orange_group     2021-10-29    1.24      kg 
     fruit      apples    egremont_russet       2021-10-29    1.27      kg 
     fruit      apples    braeburn              2021-10-29    1.12      kg 

% Create boxchart
b = boxchart(removecats(apples.variety),apples.price);
b.Parent.TickLabelInterpreter = "none";

[Achuan Chen]

Wow thank you sir! People like you mean so much to Matlab newbies like us, your code is 100times more efficient and nicer-looking than mine.

[Rebecca Stone]

If one of the categories is empty, how can we leave a space for the category that is missing/empty?

[Walter Roberson]

@Rebecca Stone

There are two possibilities I see:

• you can use setcats() https://www.mathworks.com/help/matlab/ref/categorical.setcats.html . You would do this if you know ahead of time all of the valid categories, and want to discard anything not on the list and provide space for anything on the list that does not happen to have an entry in the data
• If you want to make sure that specific categories are represented without removing any categories you did not know about in advance, then you can use addcats() https://www.mathworks.com/help/matlab/ref/categorical.addcats.html . It is not documented, but my tests show that adding in an existing category is permitted and does not change the values -- so you do not need to filter out the categories already present before addcats()

Once you have done one of the above in order to add in missing categories, then reordercats() https://www.mathworks.com/help/matlab/ref/categorical.reordercats.html to get the categories in the order you want . If you want unexpected categories to be handled (present in the data) then you will need to create some logic to decide where they should go relative to the categories you do expect.

Answer 2

[Achuan Chen]

Nevermind lol, think I'ved solved it using the cell2mat funciton. Cheers.