How to use if/then to assign a year to a set of dates?

Question

Macy 2023-2-6

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https://ww2.mathworks.cn/matlabcentral/answers/1907570-how-to-use-if-then-to-assign-a-year-to-a-set-of-dates

评论： Les Beckham 2023-2-7

Data1.xlsx

I would like to add a new vector called "school_year" that assigns a year to each point. In this case, a school year will be considered as starting August 1 and ending the following year in July 31st. For example, August 1st, 2000 - July 31st, 2001 should be assigned as school year 2001.

I want to use an if/then based on the month/year to generate the "school_year" value for each data point. A hint I have been given in this assignment is to use an if/then statement, for example, if it is after July, then what?

So in this table, there would be a new column called school_year that should read the following:

2001

2002

table_a = readtable('Data1.xlsx')
table_a = 9×4 table
    month    day    year    students
    _____    ___    ____    ________

      8       7     2000       12   
      9       8     2000       14   
      9       9     2000       13   
      3      11     2001       11   
      8       3     2001       17   
     12      15     2001       14   
      2       2     2002       10   
      5       1     2002        9   
      7       3     2002       16   

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Answer 1

Les Beckham 2023-2-6

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https://ww2.mathworks.cn/matlabcentral/answers/1907570-how-to-use-if-then-to-assign-a-year-to-a-set-of-dates#answer_1165055

编辑：Les Beckham 2023-2-6

在 MATLAB Online 中打开

table_a = readtable('https://www.mathworks.com/matlabcentral/answers/uploaded_files/1286455/Data1.xlsx')
table_a = 9×4 table
    month    day    year    students
    _____    ___    ____    ________

      8       7     2000       12   
      9       8     2000       14   
      9       9     2000       13   
      3      11     2001       11   
      8       3     2001       17   
     12      15     2001       14   
      2       2     2002       10   
      5       1     2002        9   
      7       3     2002       16   
table_a.date = datetime(table_a.year, table_a.month, table_a.day)
table_a = 9×5 table
    month    day    year    students       date    
    _____    ___    ____    ________    ___________

      8       7     2000       12       07-Aug-2000
      9       8     2000       14       08-Sep-2000
      9       9     2000       13       09-Sep-2000
      3      11     2001       11       11-Mar-2001
      8       3     2001       17       03-Aug-2001
     12      15     2001       14       15-Dec-2001
      2       2     2002       10       02-Feb-2002
      5       1     2002        9       01-May-2002
      7       3     2002       16       03-Jul-2002
schoolyear = zeros(size(table_a.date));
schoolyear(isbetween(table_a.date, '01-Aug-2000', '31-Jul-2001')) = 2001;
schoolyear(isbetween(table_a.date, '01-Aug-2001', '31-Jul-2002')) = 2002;
table_a.schoolyear = schoolyear
table_a = 9×6 table
    month    day    year    students       date        schoolyear
    _____    ___    ____    ________    ___________    __________

      8       7     2000       12       07-Aug-2000       2001   
      9       8     2000       14       08-Sep-2000       2001   
      9       9     2000       13       09-Sep-2000       2001   
      3      11     2001       11       11-Mar-2001       2001   
      8       3     2001       17       03-Aug-2001       2002   
     12      15     2001       14       15-Dec-2001       2002   
      2       2     2002       10       02-Feb-2002       2002   
      5       1     2002        9       01-May-2002       2002   
      7       3     2002       16       03-Jul-2002       2002   

If you have more data than just this small sample, the hard-coded statements above that set the schoolyear could be replaced with code like this:

found_years = unique(table_a.year);
for i = 1:numel(found_years)
    schoolyear(isbetween(table_a.date, sprintf('01-Aug-%d', found_years(i)-1), sprintf('31-Jul-%d', found_years(i)))) = found_years(i);
end
schoolyear
schoolyear = 9×1
        2001
        2001
        2001
        2001
        2002
        2002
        2002
        2002
        2002

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Les Beckham 2023-2-7

编辑：Les Beckham 2023-2-7

在 MATLAB Online 中打开

That's pretty close. With a few changes, your code will work. Obviously, the version without the loop and if test is simpler and takes advantage of the ability of Matlab to operate on vectors and matrices all at once (hence the name Matlab for matrix laboratory).

table_a = readtable('https://www.mathworks.com/matlabcentral/answers/uploaded_files/1286455/Data1.xlsx')
table_a = 9×4 table
    month    day    year    students
    _____    ___    ____    ________

      8       7     2000       12   
      9       8     2000       14   
      9       9     2000       13   
      3      11     2001       11   
      8       3     2001       17   
     12      15     2001       14   
      2       2     2002       10   
      5       1     2002        9   
      7       3     2002       16   
schoolyear = zeros(size(table_a.month)); % pre-allocate a vector the same size as table_a.month
for i = 1:numel(table_a.month) % numel tells how many elements (months) there are
    if table_a.month(i) >= 8 % address individual elements using the loop index (i)
        schoolyear(i) = table_a.year(i) + 1;
    else % don't need the elseif, just use else
        schoolyear(i) = table_a.year(i);
    end
end
table_a.schoolyear = schoolyear
table_a = 9×5 table
    month    day    year    students    schoolyear
    _____    ___    ____    ________    __________

      8       7     2000       12          2001   
      9       8     2000       14          2001   
      9       9     2000       13          2001   
      3      11     2001       11          2001   
      8       3     2001       17          2002   
     12      15     2001       14          2002   
      2       2     2002       10          2002   
      5       1     2002        9          2002   
      7       3     2002       16          2002   

Macy 2023-2-7

Thank you @Les Beckham for explaining that in depth, I learned many new functions, and I will include both methods in my assignment!

Les Beckham 2023-2-7

You are quite welcome.

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Answer 2

John D'Errico 2023-2-6

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1907570-how-to-use-if-then-to-assign-a-year-to-a-set-of-dates#answer_1165045

编辑：John D'Errico 2023-2-6

在 MATLAB Online 中打开

Data1.xlsx

Easy peasy. :)

data = [8	7	2000	12
8	2000	14
9	2000	13
11	2001	11
3	2001	17
15	2001	14
2	2002	10
1	2002	9
3	2002	16];

You have year as the third column there. I'll call it trueyear. Just create a variable, call it schoolyear.

schoolyear = trueyear + (month >= 8);

Will that work? Of course. The school year is ALWAYS the same as the trueyear when you are in the first part of the year, so between January 1 and July 31. Once the month goes into month #8, this adds 1 to the trueyear.

There is no if statement required.

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Walter Roberson 2023-2-7

table_a.school_year = schoolyear(:) ;

Macy 2023-2-7

@Walter Roberson Thank you so much :)

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