JMP 15 assumes an l-value is a column name. This was not the behavior in earlier versions. Is this intended or is it a bug?
To reproduce:
dt=new table("test"); dt<<new column("a"); a=1;
This gives an error in JMP 15 but not in JMP 14.
When I startup new sessions in JMP 14.3 and JMP 15.1 and run your script, I get the same error in both versions
Cannot set value for the column 'a' because the row number (0) is not valid.
Interesting. When I run it in 14.3.0 I do not get the error. I do not have earlier versions installed.
you need
names default to here(1);
it's annoying - I don't know if it is intentional; I would prefer it if variables were only scoped as column name if prefixed with a colon (i.e. :a).
I think the behavior depends if global:a already exists. It is annoying.
I also ran this incorrectly in version 14.3.
The only way to avoid this error is to remember that the variable name cannot be the same as the column name.
@lwx228 is incorrect. One can have a variable and a column with the same name. It is actually just a matter of scoping the name correctly, so JMP knows which you are talking about
Take the following script
dt=new table("Example", new column("A") ); dt << add rows(1); a = 13; :: a =47; :a[1] = a; show(a,::a,:a[1],dt:a[1]);
It results in
a = 47; a = 47; :A[1] = 47; dt:a[1] = 47;
What is going on here is that actually, all variables and columns have a 2 part name, separated by a colon ":"
namespace:name
and by default, if only a name is given such as in the assignment statement
a = 13;
it is assumed that "a" is a variable. If a colon is placed in front of the variable name,
:a[1] = a;
it is assumed one is referring to a column. In the above example the 1st row in the column named "a" will be given the current value (13) of the variable named "a".
One can also provide the complete 2 part name for a variable and a column.
For variables, the default namespace (first part of the name) is called ":". That's right, a colon, so the full proper name for the variable "a" is
::a
you can see the results of using the full name in the Show() statement and it's results
The full proper name for a column in this little script, is made up of the pointer variable assigned to the data table, and the actual data table column name
dt:a
The Show() statement also illustrates the 2 part name usage for a column
I hope this has not just confused everyone, but instead has given some insight
Hi txnelson
Thanks for the great explanation. Had not thought about the first : in :: to refer to the global namespace. I must have been wrong with 14.3. When I try now, I get the warning too.
You wrote "and by default, if only a name is given such as in the assignment statement".
This is also what I expected, but if a column in a data table has the same name, JMP clearly assumes it should assign the value to the column.
Seems names default to here(1) fixes that behaviour as David pointed out. I always waited with defaulting names to the here namespace because it makes debugging more cumbersome. But from now on, I will always use this option from the start!
I hope the JMP team will change that behaviour, because it can create some really hard to find bugs! Especially, if a script actually refers to columns without :'s !
