Expression with empty doc property to sum columns if they exist

[Przemek Stasica]

Hi I'm trying to create a calculated column to sum values from 2 columns but only if they exist in a table.

It seems the expressison is always preevaluated when setting up so the engine disallows it.

This is contrary to Spotfire troubleshooting guide which seems to be advising this is possible.

e.g.Sum(10, [${EmptyProperty}])

But in reality when propery is empty I'm getting "Could not find column" message.

I need something to allow me to work with columns but only if they exist.

Any ideas

Many thanks

[Gaia Paolini]

You could try to create the column with an Iron Python script

This worked for me. Even though the system threw an exception, the calculated column is created and empty. I used the 'iris' dataset as example. However if I then try to edit it via Data>Column Properties, it shows as red.

 

from Spotfire.Dxp.Data import CalculatedColumn

 

col1='Sepal_Length'

col2='NonExistentColumn'

expression = '['+col1+'] + ['+col2+']'

print (expression)

colname='MyNewColumn'

 

cols = Document.Data.Tables["iris"].Columns

 

if cols.TryGetValue(colname)[0] == True:

pass

print('column ',colname,'already exists')

else:

try:

cols.AddCalculatedColumn(colname,expression);

except:

pass

 

#check column was created anyway

for cc in Document.Data.Tables["iris"].Columns:

print (cc.Name)