Applying nested conditions in q

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1

I want to add a column to an existing table based on nested conditions

T:(a:FR;b:10 20;c:9 21;d:10 22)

Func:{[tab]

 If a=`F

     If b<c 

         Add new column with value as 'hi

      Else

          new='welcome

  Else

           if  c>d

                new=`hi

            Else

                new='welcome

}

Please help.

2

This is most easily done in two parts and then defaulting the rest to welcome:

 

 

q)T:update newCol:hi from T where a=F,b<c q)T:update newCol:hi from T where a&lt;&gt;F,c>d q)T:update`welcome^newCol from T q)T a b c d newCol ------------------ F 10 9 10 welcome R 20 21 22 welcome

 

 

You may find the reference on update statements useful: https://code.kx.com/q/ref/update/ 

If you want it done in one line (which doesn’t scale well for any additional clauses you might want):

 

 

q)update newCol:welcomehi any(all(a=F;b&lt;c);all(a&lt;&gt;F;c>d))from T a b c d newCol ------------------ F 10 9 10 welcome R 20 21 22 welcome

 

 

3

Thanks Cillian. 

4

Another option is to use vector conditional (?)

https://code.kx.com/q/ref/vector-conditional/

q)update new_col:?[a=`F;[?[b<c;`hi;`welcome]];[?[c>d;`hi;`welcome]]] from T a b c d new_col ------------------ F 10 9 10 welcome R 20 21 22 welcome