Combine Shared Columns with Plus-Join

Question

Using the same t and codes2 (with its age:100 column) from the previous question, how would you add the age column from both tables together, rather than having one overwrite the other?

t:([] names:`Tom`Mary`Jack`Sean`Anne`Roy;
      country:`Ireland`England`France`England`Germany`Scotland;
      age:10 13 14 18 21 41;
      employed:101101b)

codes:([] Country:`Ireland`England`France`Germany`Scotland;
          digits:("+353";"+44";"+33";"+49";"+44"))
codes2:`country xcol update age:100 from codes

Solution

t pj 1!codes2

names country  age employed digits
----------------------------------
Tom   Ireland  110 1        "+353"
Mary  England  113 0        "+44"
Jack  France   114 1        "+33"
Sean  England  118 1        "+44"
Anne  Germany  121 0        "+49"
Roy   Scotland 141 1        "+44"

Explanation

pj (plus-join) behaves like a left join, except that for columns present in both tables it adds the right table's values to the left's instead of overwriting them. t's original age values (10, 13, 14, 18, 21, 41) are each increased by 100, the value from codes2, giving 110, 113, 114, 118, 121, 141. digits exists only in codes2, so it is simply added as a new column.

Be careful when both tables share a non-numeric column. If t already had a digits column (for example after running t:t lj 1!country xcol codesfrom the earlier question),pjwould try to add the two string columns together and fail with'type`. In that case, drop the column from the right table first: t pj 1!delete digits from codes2.