function not working properly

[Sam]

I am confused with this:  Look at this below. Why are the lines in bold yielding different results?

q)trade

date       open  high  low   close volume   sym

------------------------------------------------

2006.10.03 24.5  24.51 23.79 24.13 19087300 AMD

2006.10.03 27.37 27.48 27.21 27.37 39386200 MSFT

2006.10.03 24.1  25.1  23.95 25.03 17869600 AMD

2006.10.03 27.39 27.96 27.37 27.94 82191200 MSFT

2006.10.03 24.8  25.24 24.6  25.11 17304500 AMD

2006.10.03 27.92 28.11 27.78 27.92 81967200 MSFT

2006.10.03 24.66 24.8  23.96 24.01 17299800 AMD

2006.10.03 27.76 28    27.65 27.87 36452200 MSFT

q)extr

{[t;c;r] select from t where (`$1#'string c) within r}

q)

q)

q)extr[trade;sym;`K`Z]

date       open  high  low   close volume   sym

------------------------------------------------

2006.10.03 27.37 27.48 27.21 27.37 39386200 MSFT

q)

q)

q)select from trade where (`$1#'string sym) within `K`Z

date       open  high  low   close volume   sym

------------------------------------------------

2006.10.03 27.37 27.48 27.21 27.37 39386200 MSFT

2006.10.03 27.39 27.96 27.37 27.94 82191200 MSFT

2006.10.03 27.92 28.11 27.78 27.92 81967200 MSFT

2006.10.03 27.76 28    27.65 27.87 36452200 MSFT

[Bohák András]

Hi Sam,
you can not use an input of the function as a col name in a query like this. What happens when you run "extr[trade;sym;`K`Z]" is that the existing variable named sym will be passed to the function. Try "extr[trade;open;`1`5]", it will not even run, if you do not have "open" defined (you will get 'open).
The only way (that I know) to have a query with a dynamic column name is to use the functional form of select. This will work as intended:

extr:{?[x;enlist (within;($;enlist `;((';#);1;(string;y)));enlist z);0b;()]}

When you write functional forms it is usually a huge help to parse the query in q and write the functional form based on the result.
Note that the enlist before "z" is necessary because otherwise q would interpret `K`Z (or whatever limits) as column names.

Best,
Andras

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[Sam]

Thanks for the information. It makes sense to me. How do I view functional form of query generated by Q?

thanks,

Sam

[Sam]

I found the function 'parse'. Thanks. This is helpful.

[Bohák András]

parse "select from trade where (`$1#'string sym) within `K`Z"

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