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Meet the Zen monks
In Jeff Borrors classic textbook Q for Mortals you will find frequent references to moments of Zen meditation leading to flashes of insight into the workings of q.
My teacher Myokyo-ni liked to quote Dogen-zenji:
The Great Way is not difficult. It avoids only picking and choosing.
The Do form of the Scan iterator has a pattern I think of as the Zen monks.
How many Zen monks does it take to change a lightbulb?
Two. One to change it; one not to change it.The basic pattern is to apply a function and not to apply it. Consider the
trimkeyword. It must find the spaces in a string, then the continuous spaces from each end. If we had to writetrimin q it might beq){b:x<>" ";(b?1b)_ neg[reverse[b]?1b] _ x}" Trim the spaces. " "Trim the spaces."We notice the repetitions:
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bandreverse[b]are searched for1b - two uses of the Drop operator
We want to do the search/drop thing from both ends of the string.
q){x{y _ x}/1 -1*(1 reverse" "<>x)?'1b}" Trim the spaces. " "Trim the spaces."Notice the
{y _ x}reduction above. Lambda{y f x}commutes a functionfby switching its arguments. The patternR{y f x}/Lsuccessively applies a list of left argumentsLto an argumentR.Here we use
1 reverseto get the boolean vector and its reversal. I think of this1 fpattern as the Zen monks.Here is another use for it, in finding the shape (rows and columns) of a matrix.
q)show m:{max[count each x]$'x}string`avoids`picking`and`choosing "avoids " "picking " "and " "choosing" q)shp:{count each 1 firstx} / shape of a matrix q)shp m 4 8The Zen Buddhist pension plan: A day without work is a day without food. Can you see any other work for the monks?
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3 Replies
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This 1 f pattern is crazy, but i love it
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Such a great post – so interesting!
Thanks for sharing @SJT
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