kdb - KDB Apply logic where column exists - data validation - kdb

Question

I'm trying to perform some simple logic on a table but I'd like to verify that the columns exists prior to doing so as a validation step. My data consists of standard table names though they are not always present in each data source.
While the following seems to work (just validating AAA at present) I need to expand to ensure that PRI_AAA (and eventually many other variables) is present as well.
t: $[`AAA in cols `t; temp: update AAA_VAL: AAA*AAA_PRICE from t;()]
Two part question
This seems quite tedious for each variable (imagine AAA-ZZZ inputs and their derivatives). Is there a clever way to leverage a dictionary (or table) to see if a number of variables exists or insert a place holder column of zeros if they do not?
Similarly, can we store a formula or instructions to to apply within a dictionary (or table) to validate and return a calculation (i.e. BBB_VAL: BBB*BBB_PRICE.) Some calculations would be dependent on others (i.e. BBB_Tax_Basis = BBB_VAL - BBB_COSTS costs for example so there could be iterative issues.
Thank in advance!

Answer 1

A functional update may be the best way to achieve this if your intention is to update many columns of a table in a similar fashion.
func:{[t;x]
if[not x in cols t;t:![t;();0b;(enlist x)!enlist 0]];
:$[x in cols t;
![t;();0b;(enlist`$string[x],"_VAL")!enlist(*;x;`$string[x],"_PRICE")];
t;
];
};
This function will update t with *_VAL columns for any column you pass as an argument, while first also adding a zero column for any missing columns passed as an argument.
q)t:([]AAA:10?100;BBB:10?100;CCC:10?100;AAA_PRICE:10*10?10;BBB_PRICE:10*10?10;CCC_PRICE:10*10?10;DDD_PRICE:10*10?10)
q)func/[t;`AAA`BBB`CCC`DDD]
AAA BBB CCC AAA_PRICE BBB_PRICE CCC_PRICE DDD_PRICE AAA_VAL BBB_VAL CCC_VAL DDD DDD_VAL
---------------------------------------------------------------------------------------
70 28 89 10 90 0 0 700 2520 0 0 0
39 17 97 50 90 40 10 1950 1530 3880 0 0
76 11 11 0 0 50 10 0 0 550 0 0
26 55 99 20 60 80 90 520 3300 7920 0 0
91 51 3 30 20 0 60 2730 1020 0 0 0
83 81 7 70 60 40 90 5810 4860 280 0 0
76 68 98 40 80 90 70 3040 5440 8820 0 0
88 96 30 70 0 80 80 6160 0 2400 0 0
4 61 2 70 90 0 40 280 5490 0 0 0
56 70 15 0 50 30 30 0 3500 450 0 0
As you've already mentioned, to cover point 2, a dictionary of functions might be the best way to go.
q)dict:raze{(enlist`$string[x],"_VAL")!enlist(*;x;`$string[x],"_PRICE")}each`AAA`BBB`DDD
q)dict
AAA_VAL| * `AAA `AAA_PRICE
BBB_VAL| * `BBB `BBB_PRICE
DDD_VAL| * `DDD `DDD_PRICE
And then a slightly modified function...
func:{[dict;t;x]
if[not x in cols t;t:![t;();0b;(enlist x)!enlist 0]];
:$[x in cols t;
![t;();0b;(enlist`$string[x],"_VAL")!enlist(dict`$string[x],"_VAL")];
t;
];
};
yields a similar result.
q)func[dict]/[t;`AAA`BBB`DDD]
AAA BBB CCC AAA_PRICE BBB_PRICE CCC_PRICE DDD_PRICE AAA_VAL BBB_VAL DDD DDD_VAL
-------------------------------------------------------------------------------
70 28 89 10 90 0 0 700 2520 0 0
39 17 97 50 90 40 10 1950 1530 0 0
76 11 11 0 0 50 10 0 0 0 0
26 55 99 20 60 80 90 520 3300 0 0
91 51 3 30 20 0 60 2730 1020 0 0
83 81 7 70 60 40 90 5810 4860 0 0
76 68 98 40 80 90 70 3040 5440 0 0
88 96 30 70 0 80 80 6160 0 0 0
4 61 2 70 90 0 40 280 5490 0 0
56 70 15 0 50 30 30 0 3500 0 0

Answer 2

Here's another approach which handles dependent/cascading calculations and also figures out which calculations are possible or not depending on the available columns in the table.
q)show map:`AAA_VAL`BBB_VAL`AAA_RevenueP`AAA_RevenueM`BBB_Other!((*;`AAA;`AAA_PRICE);(*;`BBB;`BBB_PRICE);(+;`AAA_Revenue;`AAA_VAL);(%;`AAA_RevenueP;1e6);(reciprocal;`BBB_VAL));
AAA_VAL | (*;`AAA;`AAA_PRICE)
BBB_VAL | (*;`BBB;`BBB_PRICE)
AAA_RevenueP| (+;`AAA_Revenue;`AAA_VAL)
AAA_RevenueM| (%;`AAA_RevenueP;1000000f)
BBB_Other | (%:;`BBB_VAL)
func:{c:{$[0h=type y;.z.s[x]each y;-11h<>type y;y;y in key x;.z.s[x]each x y;y]}[y]''[y];
![x;();0b;where[{all in[;cols x]r where -11h=type each r:(raze/)y}[x]each c]#c]};
q)t:([] AAA:1 2 3;AAA_PRICE:1 2 3f;AAA_Revenue:10 20 30;BBB:4 5 6);
q)func[t;map]
AAA AAA_PRICE AAA_Revenue BBB AAA_VAL AAA_RevenueP AAA_RevenueM
---------------------------------------------------------------
1 1 10 4 1 11 1.1e-05
2 2 20 5 4 24 2.4e-05
3 3 30 6 9 39 3.9e-05
/if the right columns are there
q)t:([] AAA:1 2 3;AAA_PRICE:1 2 3f;AAA_Revenue:10 20 30;BBB:4 5 6;BBB_PRICE:4 5 6f);
q)func[t;map]
AAA AAA_PRICE AAA_Revenue BBB BBB_PRICE AAA_VAL BBB_VAL AAA_RevenueP AAA_RevenueM BBB_Other
--------------------------------------------------------------------------------------------
1 1 10 4 4 1 16 11 1.1e-05 0.0625
2 2 20 5 5 4 25 24 2.4e-05 0.04
3 3 30 6 6 9 36 39 3.9e-05 0.02777778
The only caveat is that your map can't have the same column name as both the key and in the value of your map, aka cannot re-use column names. And it's assumed all symbols in your map are column names (not global variables) though it could be extended to cover that
EDIT: if you have a large number of column maps then it will be easier to define it in a more vertical fashion like so:
map:(!). flip(
(`AAA_VAL; (*;`AAA;`AAA_PRICE));
(`BBB_VAL; (*;`BBB;`BBB_PRICE));
(`AAA_RevenueP;(+;`AAA_Revenue;`AAA_VAL));
(`AAA_RevenueM;(%;`AAA_RevenueP;1e6));
(`BBB_Other; (reciprocal;`BBB_VAL))
);