The If() function evaluates the first result expression when its condition evaluates as true (a nonzero or nonmissing value). Otherwise, it evaluates the second result expression.
The syntax is:
If ( condition, result1, result2 );
For example, the following script returns "Young" when the age is less than 12. Otherwise, the script returns "Young at Heart".
dt = Open( "$SAMPLE_DATA/Big Class.jmp" );
dt << New Column( "age group", "Character" );
For Each Row(
:age group = If( :age <= 12,
"Young",
"Young at Heart"
)
);
You can also string together multiple conditions and results. The syntax is:
If( condition1, result1,
condition2, result2,
...,
resultElse );
In the preceding example, if condition1 is not true, the function continues evaluating until it finds a true condition. Then that condition’s result is returned.
The last result is returned when all conditions are false. And when a value is missing, the missing value is returned. For these reasons, it’s very important to include a default result at the end of the expression. Consider the following example, which recodes gender abbreviations in Big Class.jmp:
dt = Open( "$SAMPLE_DATA/Big Class.jmp" );
For Each Row( sex =
If(
sex == "F", "Female",
sex == "M", "Male",
"Unknown" );
);
The script works like this:
|
For Each Row( sex = |
For each row in the table, sex is the column that is recoded. |
|
If( |
Begins the If() loop. |
|
sex == "F", "Female", |
If the value of sex is F, replaces the value with Female. |
|
sex == "M", "Male", |
If the value of sex is M, replaces the value with Male. |
|
"Unknown" ); |
If neither of the above conditions are true, replaces the value with Unknown. If this result were omitted and the value of sex were missing, the script would return a missing value. |
|
); |
Ends the loop. |
You can also put actions and assignments in the result expression. The following example assigns 20 to x, because the first condition (y < 20) is false:
y = 25;
z = If( y < 20, x = y, x = 20 );
Note: Be careful to use two equal signs (==) for equality tests, not one equal sign (=). An If with an argument such as name=value assigns rather than tests the value.
Running a script that contains dozens of If() Statements can cause memory problems. We recommend reducing the If() nesting. Suppose that your script contains 100 If() statements in this format:
If( val, If( val, If( val, If( val, If( val,
If( val, If( val, If( val, If( val, If( val,
...
) ) ) ) ) ) ) ) ) );
Rewrite the script as follows:
If( val, val1, If(val, val2, If( val, val3,
If( val, val4, If( val, val5, If( val, val6, ...) ) ) ) ) );
You can also try setting the maximum call depth. The Maximum Call Depth preference sets the default for the maximum call depth (or stack size) in which JSL built-in functions, user-defined functions, or Recurse() function calls can be made. By default, the maximum call depth is set to 256.
In JMP, your JSL script has a limited amount of physical runtime stack memory in which to perform JSL function calls. By default, this size is set to 2MB. Increasing the maximum call depth can cause a physical runtime stack overflow, so incrementally increase this preference in small amounts until you find the best value that works for your JSL script.
Preferences[1] << Set( Maximum JMP call depth( 64 ) );