How to use if/then to create a vector using values from a table.

Hi, I am new to MatLab and coding in general. Here, I wish to assign a "schoolyear" to each data point. If the table_a.month falls on or after August, schoolyear is equal to the year plus 1. Hence why the code depends on month>=8 (August is the 8th month of the year). The following code gives me the correct values for schoolyear, but is this the proper way to use if/then to create the schoolyear vector? Is there another way you would do it using if/then?

Also two more simple questions: How can I display schoolyear as an 8x1 column in a matrix? And, how can I add schoolyear as a variable to table_a?

Thank you.

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   

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

schoolyear

schoolyear = 1×8

2001 2001 2001 2001 2002 2002 2002 2002

Answer 1

[Voss]

"is this the proper way to use if/then to create the schoolyear vector? Is there another way you would do it using if/then?"

Looks ok to me, except I would pre-allocate the schoolyear vector (see below).

"How can I display schoolyear as an 8x1 column in a matrix?"

If you want to display schoolyear as a column vector:

schoolyear(:)

If you want schoolyear to be a column vector, one way is to pre-allocate it as such:

table_a = readtable('Data1.xlsx');

% pre-allocate a column vector of zeros:
schoolyear = zeros(height(table_a),1);

% then the loop itself is the same:
for i = 1:height(table_a)
    if table_a.month(i)>=8
        schoolyear(i) = table_a.year(i) + 1;
    else
        schoolyear(i) = table_a.year(i);
    end
end

% now schoolyear is a column vector containing your values:
schoolyear

schoolyear = 9×1

2001 2001 2001 2001 2002 2002 2002 2002 2002

"how can I add schoolyear as a variable to table_a?"

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 @Voss!

[Voss]

You're welcome!

Answer 2

[Amal Raj]

Hi Macy,

Because it avoids the loop, this is an efficient method of obtaining your desired table.

table_a = readtable('Data1.xlsx');

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

table_a = addvars(table_a, schoolyear, 'After', 'students', 'NewVariableNames', 'schoolyear');

disp(table_a);