Error message for single valued column comes too early

[jtpesone]

The error message about all values (rows) in a column being the same comes too early, as this kind of a column might be excluded by the user. The error should only be initiated after generating the input for SOM. Or it could be a warning in the Data preparation stage and then an Error once data has been prepared.

[jtpesone]

I could not reproduce this. Now the error comes only when pressing NEXT in the data input window, and if the constant column is excluded, the program proceeds as it should. This behavior is fine, and this issue might be redundant.