Hi all,

Say if I have a data table which consists of 4 column: itemID, location and
price, which location is a text field and itemID and location together forms
the primary keys.

when I tried to run setkey (DT, itemID, location), I got the following
message:

Error in setkey (DT, itemID, location) :
  All keyed columns must be storage mode integer

Is there any way I could define a non-numerical field (in this case
location) to be the key?

Also, if I do not use the location as a key, will I still able to merge 2
data tables based on itemID and location using the "merge" method in
data.table?

Thanks a lot!

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