Sorry for the basic question.

I have a dataset with 100-variable list from v1-v100 with >10k observations. I would like to create a new column to indicate if a certain value is present for each observation and if it does, which variable this value belongs to.

For example, if the value of interest is "water", for observation #1, if "water" appears on v2, I would like to assign 2 for observation #1....

Any value appears only once in v1-v100, if any.

Thank you, everyone.