Want to weight Histogram entries by value

I am using a nx2 array to populate a Histogram

23 2

12 2

85 3

38 3

12 4

09 2

97 4

and want a histogram (or bar chart?) with second attribute as the X axis and the first attribute to be summed up rather then the elements just counted, so the hist would plot

44 2

123 3

111 4

Rather than

3 2

2 3

2 4

Can you help suggest how to use BAR or HISTOGRAM to achieve this please?

Many thanks

Answer 1

[Voss]

data = [
    23    2
    12    2
    85    3
    38    3
    12    4
    09    2
    97    4
    ];

[groups,group_ids] = findgroups(data(:,2))

groups = 7×1

1 1 2 2 3 1 3

group_ids = 3×1

2 3 4

totals = splitapply(@(x)sum(x(:,1)),data,groups)

totals = 3×1

44 123 109

bar(group_ids,totals)

[simon lumsdon]

Thank you very much, extremely helpful!

[Voss]

You're welcome! Any questions, let me know. Otherwise, please "Accept This Answer". Thanks!

[Vlatko Milic]

Hi @Voss and @Steven Lord,

Do you have any idea of how I could make the corresponding procedure but with set intervals on the x-axis, i.e. 2.5-3.5 etc.? Your solution is quite close to what I want to accomplish, but without the intervals...

Answer 2

[Steven Lord]

data = [
    23    2
    12    2
    85    3
    38    3
    12    4
    09    2
    97    4
    ];

[V, G] = groupsummary(data(:, 1), data(:, 2), @sum)

V = 3×1

44 123 109

G = 3×1

2 3 4