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Applying nested conditions in q
I want to add a column to an existing table based on nested conditions
T:([]a:`F`R;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.
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2 Replies
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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<>`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:`welcome`hi any(all(a=`F;b<c);all(a<>`F;c>d))from T a b c d newCol ------------------ F 10 9 10 welcome R 20 21 22 welcome
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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
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