How is your column data joined ? with a "space" or with a "coma"?
You can use the split() function:
split(<your field data>,<your separator>
For example if the field contains "Big,Small"
To get the first value "Big"
You can do a split("Big,Small",",").getValue(0).ToString --Not sure if the index begins with 0 or 1 / have to test it
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