New to Matlab. I need help with group (?), double counting, and so on. Thank you!

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JB 2020-6-4

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评论： JB 2020-6-4

采纳的回答： Image Analyst

New to Matlab, I need your help.

Suppose my data is this:

schoolid classid classsize enrollment

1001 1 10 22

1001 2 12 22

1005 1 14 29

1005 2 15 29

1018 1 8 22

1018 2 4 22

1018 3 10 22

.

And I want to find:

a. number of schools.

I found this one by

grps = findgroups(schoolid);

n = max(grps);

b. the average number of classes in a school.

I know how to solve by hand, but you know, my data is big,,, help me with codes please.

c. Provide the histogram of enrollment, and report its mean, median, max and min.

I know codes to find histogram, mean, and so on,

but you see the enrollemnt column is a double counting, I need to figure this out frist.

Please help me... Matlab geniuses... Thank you!

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Rik 2020-6-4

Have you looked at the splitapply function?

JB 2020-6-4

I will look into it. Thanks!

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Answer 1

Image Analyst 2020-6-4

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For a, and alternate way is

numberOfSchools = length(unique(schoolid))

A for loop way for b and c is

us = unique(schoolid)
numRows = length(schoolid)
for k = 1 : length(us)
    thisSchoolsRows = schoolid == us(k); % Only rows with this particular school
    numClasses(k) = length(thisSchoolsRows) % Assumes each classid's are unique and show up in only one row for a particular school.
end
aveClassesOverAllSchools = numClasses(k) / numberOfSchools