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

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

2001

2001

2001

2002

2002

2002

2002

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   

Answer 1

[Les Beckham]

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

[Macy]

Thank you! Yes this is a sample set of data a part of a much larger set. How can this be altered to use the month and year vectors and not make the "date" vector. So if it's after July, then ?

This was reccomended to me by my professor to split the date into 3 columns and use them in the if/then, although your method works great too.

[Les Beckham]

John's answer is simpler than mine and doesn't require creating the date vector or any loop.

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.schoolyear = table_a.year + (table_a.month >= 8)

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]

Ah I see ok, thank you. I want to use an if/then just to see how it would work (reccomended by my professor to try it out).

I'm trying to write it out like so, but I don't really know how to code. Is this even the right idea when my prof says to use an if/then?

for i = 1:??
    if table_a.month>=8
        schoolyear = table_a.year + 1
    elseif table_a.month<7
        schoolyear = year
    end
end
schoolyear

I'm also not sure how to creat the schoolyear vector in the first place.

[Les Beckham]

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]

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]

You are quite welcome.

Answer 2

[John D'Errico]

Easy peasy. :)

data = [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];

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.

[Macy]

Nice, this is a very smart way to think about it!

For my assignment this gets the job done, although do you know how I could do it using the if statement just so I can see how it's done, as the hint we were given in the assignment was to use an if statement, although as I see here it's not required to accomplish the same task.

[Macy]

Like using the same idea I am thinking of this, but I don't know how to code it properly (I am very new to matlab).

for i = 1:??
    if month>=8
        schoolyear = year + 1
    elseif month<8
        schoolyear = year
    end
end

[Walter Roberson]

You would want to loop over the valid row indices into the table; see height

For variables such as month you would need to index according to the current row index.

You will find it easiest to generate all of the outputs first and add that entire output as a table variable, instead of assigning into the table as you go... unless, that is, you first generate a full-sized variable of default values.

[Macy]

Got it, thank you @Walter Roberson. I generated the outputs first like you suggested and got the code below. In this code, is school year vector? How can I make it a column in a matrix?

for i = 1:table_a.month
if table_a.month(i)>=8
    schoolyear(i) = table_a.year(i) + 1;
else
    schoolyear(i) = table_a.year(i);
end
end
schoolyear

[Walter Roberson]

table_a.school_year = schoolyear(:) ;

[Macy]

@Walter Roberson Thank you so much :)