Determining if a column exists

[#1]

I have a JMP script that creates a new column with a formula in it. I'm trying to find out how to detect if the column already exists so that I can skip creating it, and avoid generating extra columns. I'm sure it's there, but I'm not finding it in the literature that I have.

Thanks.

Mike

[#2 · Accepted solution]

dt = open("$sample_data\Big Class.jmp");
 
col_name_list = dt << get column names(string);
 
new_column = "BMI";
 
// English BMI Formula
// BMI = ( Weight in Pounds / ( Height in inches x Height in inches ) ) x 703
 
if (!contains(col_name_list, new_column),
      dt <<New Column("BMI", numeric, continuous,
            formula(703 * :weight / :height / :height)
      );
);

[#3]

Thanks, that works just fine for me. I was expecting to find a function to check for existance, but this works.

[#4]

There is no single function that I am aware of. But Is missing() in combination with Is Scriptable() can do the trick.

The column also need to be enclosed by a Try() statement to avoid the script from stopping if the column would not exist.

dt = Open( "$sample_data\Big Class.jmp" );
 
new_column = "BMI";
 
If( Is Missing( Is Scriptable( Try( Column( new_column ) ) ) ),
	dt << New Column( new_column, numeric, continuous, formula( 703 * :weight / :height / :height ) )
);

[#5]

Also handy to know. I'm always glad to have another tool to add to the toolbox.

Thanks.

[#6]

Thanks ms!
Only your example worked for me, because the other solution is case sensitive. I had to use yours, since I could not be sure that the case of my string characters are correct.

[#7]

Here's a version of my logic that's case-insensitive.

dt = open("$sample_data\Big Class.jmp");
col_name_list = dt << get column names(string);
// Convert all column names to uppercase for case-insensitive search
for (i = 1, i <= nitems(col_name_list), i++,
	col_name_list[i] = uppercase(col_name_list[i]);
);
new_column = "BMI";
// English BMI Formula BMI = ( Weight in Pounds / ( Height in inches^2 ) ) x 703
if (!contains(col_name_list, uppercase(new_column)),
    dt <<New Column("BMI", numeric, continuous,
            formula(703 * :weight / :height / :height)
    );
);

[#8]

I am not certain if this is true in all recent versions of JMP. I make this comment only to highlight an opportunity to improve the robustness of the code.

'Contains' returns the position of the item, which is fine to use in an 'if' statement, since zero will be interpreted as false and a positive value will be interpreted true. When preceding a contains with a not '!', the condition works when the item is not present or when present as the first item; however, when the item isn't first ( a value greater than 1 ), the not '!' can fail to convert the condition to false. This can be avoided by using a comparison '>0' with the 'contains'. See below for syntax.

dt = Open( "$sample_data\Big Class.jmp" );
 
col_name_list = dt << get column names( string );
 
new_column = "BMI";
 
// English BMI Formula
// BMI = ( Weight in Pounds / ( Height in inches x Height in inches ) ) x 703
 
If( !(Contains( col_name_list, new_column ) > 0),
	dt << New Column( "BMI", numeric, continuous, formula( 703 * :weight / :height / :height ) )
);

[#9]

That's very handy to know. I'll have to watch out for that.

Thanks

[#10]

Hello wiebepo,

I tried different combinations and negating a positive integer, no matter how large, results in a 0.  So my code will work (in JMP 9 and 10).  Having said that I appreciate the heads up - this approach might not work in all languages.  It certainly bears further testing.

b = 2000000000000;
!b;

The log shows:

0

Regards,

PMroz