How to group values to display in bar charts while doing data analysis

Question

Tessa 2020-10-30

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/631369-how-to-group-values-to-display-in-bar-charts-while-doing-data-analysis

评论： Peter Perkins 2020-11-18

I am doing some data-analysis to see some weekly totals over time. Right now I am manually creating new tables to display everything in bar-charts, but I think that there has to be a better way. I load the data from excel, the data contains cells and doubles. The analysis I want to be doing contains only doubles. (I am using Matlab R2020b)

An example of what my data looks like:

Names = {'These';'are';'some';'random';'names';'yay'};
YearWeek = [201901;201901;201901;201902;201902;201902];
Duration = rand(6,1);
 
T = table(Names,YearWeek,Duration);

T =
  6×3 table
      Names       YearWeek     Duration
    __________    _________    ________
    {'These' }    2.019e+05    0.67874 
    {'are'   }    2.019e+05    0.75774 
    {'some'  }    2.019e+05    0.74313 
    {'random'}    2.019e+05    0.39223 
    {'names' }    2.019e+05    0.65548 
    {'yay'   }    2.019e+05    0.17119 

Now I want to make a bar chart in which I want to see the sum of the duration per YearWeek.

What I am doing right now is:

%Selecting the right data
selected_columns = [T.YearWeek,T.Duration];
 
%Sum duration per week
[year_week,~,location_year_week] = unique(selected_columns(:,1));
SumOfDurationPerWeek = zeros(height(year_week),2);
for i = 1:height(year_week)
    SumOfDurationPerWeek(i,1) = year_week(i);
    SumOfDurationPerWeek(i,2) = sum(selected_columns(location_year_week == i, 2));
end
%Plot as a bar chart
figure()
bar(SumOfDurationPerWeek(:,1),SumOfDurationPerWeek(:,2))

However I cannot believe that there is no easier way.

Shouldn't it be possible to create a bar chart immediately without summing all the values?

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Answer 1

Ameer Hamza 2020-10-30

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/631369-how-to-group-values-to-display-in-bar-charts-while-doing-data-analysis#answer_529204

See retime(): https://www.mathworks.com/help/matlab/ref/timetable.retime.html

Even using splitapply() with findgroups() will be a simpler solution.

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Tessa 2020-10-30

That might be useful as well! I'll give it a try.

Thank you!

Peter Perkins 2020-11-18

If you want weekly totals, a timetable and the retime function is the most straight-forward way. But your timestamps are numeric, so you'd need to convert things like 201901 into things like datetime(2018,12,31) or datetime(2019,1,6) (depending on how you define "week of year"), so it might be easier to leave them as numeric and use groupsummary.

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