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03-15-2014 01:30 AM

Hi all,

I know that SAS has functions to get 'mean' and 'std' directly, as the following codes:

/*Rolling 24-month window*/

proc sql;

create table roll as

select

h2.cusip,

h2.monthDate as periodEndDate format=yymmd7.,

h2.ret,

mean(h1.ret) as meanRet,

std(h1.ret) as stdRet

from

have as h1 inner join

have as h2 on h1.cusip=h2.cusip and

intck("MONTH", h1.monthDate, h2.monthDate) between 1 and 24

group by h2.cusip, h2.monthDate, h2.ret

having count(h2.cusip)=24;

quit;

How about the function for 'skewness' or 'idiosyncractic skewness'?

Thanks

Accepted Solutions

Solution

03-16-2014
03:55 AM

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03-16-2014 03:55 AM

ZZb is there a reason that you must code in SQL? Do you have a third party DBMS? When you have a third-party DBMS wich one? SQL aggregated functions are as standard as babylonian languages (old tst) for the advanced ones.

I your question the same as: https://communities.sas.com/message/192004

---->-- ja karman --<-----

All Replies

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03-15-2014 05:52 AM

I believe proc Univariate gives Skewness statistics for a given variable.

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03-15-2014 06:08 AM

This wat the SAS SQL supports: SAS(R) 9.4 SQL Procedure User's Guide (summary-function) this is standard SQL not some dialect.

The SAS procedures have there origin in Stats see: Base SAS(R) 9.4 Procedures Guide, Second Edition (Keywords and Formulas)

When you are coming form some RDBMS that have implemented statistics by grouping it are native dialects.

In those cases you could benefit that SAS will do a translation (as that shoudl word) for in-database processing.

---->-- ja karman --<-----

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03-15-2014 02:57 PM

As indicated by Jaap, there isn't a SKEW function for the SAS SQL implementation.

Also, it seems weird to include your analysis variable (ret) in your Group BY statement.

You can use proc means or proc univariate to get the skewness.

**proc** **sort** data=sashelp.class out=class; by sex; **run**;

**proc** **means** data=class noprint;

by sex;

output out=summary mean(weight)=avg_ret std(weight)=std_ret skew(weight)=skew_ret;

**run**;

EDIT: to supply working example

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Posted in reply to Reeza

03-16-2014 03:21 AM

I want to get the rolling skewness. Since there is no SKEW function in SQL, I have to think about other ways.

ret meanRet stdRet SkewRet

36110 | 1985-01 | 0.16865 | 0.034400 | 0.083940 |

36110 | 1985-02 | -0.02326 | 0.041494 | 0.087867 |

36110 | 1985-03 | -0.10714 | 0.040525 | 0.088471 |

36110 | 1985-04 | -0.10027 | 0.029867 | 0.090268 |

36110 | 1985-05 | 0.11940 | 0.019866 | 0.090858 |

36110 | 1985-06 | 0.01333 | 0.015292 | 0.082216 |

36110 | 1985-07 | 0.15868 | 0.014435 | 0.082121 |

36110 | 1985-08 | 0.03429 | 0.022072 | 0.086726 |

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03-15-2014 03:58 PM

No it doesn't. Back to basics: compute your own :

**data test;**

**do x = 2,4,6,3,1;**

** output;**

** end;**

**run;**

**/* Expected : skewness(2,4,6,3,1) = 0.5901286564 */**

**proc sql;**

**select count(x) * (sum(x**3) -3*mean(x)*uss(x)+3*mean(x)**2*sum(x)-count(x)*mean(x)**3) /**

** ((count(x)-1)*(count(x)-2)*STD(x)**3) as skewness format=14.10**

**from test;**

**quit;**

PG

PG

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03-15-2014 11:50 PM

Use PROC MEANS or PROC UNIVARIATE if you want to calculate statistics. You can define your current 24 month merge as a view if you want avoid creating a large intermediate table.

**proc** **sql** ;

create view roll24 as

select h2.cusip

, h2.monthDate as periodEndDate format=yymmd7.

, h2.ret

from have as h1 inner join have as h2

on h1.cusip=h2.cusip

and intck("MONTH", h1.monthDate, h2.monthDate) between **1** and **24**

group by h2.cusip, h2.monthDate, h2.ret

having count(h2.cusip)=**24**

;

**quit**;

**proc** **means** data=roll24 ;

by cuspid periodenddate ;

var ret ;

output out=roll mean=meanRet std=stdRet skew=skewRet ;

**run**;

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03-16-2014 03:28 AM

I tried your code. It does not seem to work.

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03-16-2014 09:13 AM

The MEANS will calculate the statistics properly, you just need to fix the SQL so that it includes the values that you want to include in your calculations. It seems dubious to me to group by RET and also include RET in the returned values? Perhaps you want to group by H2.RET (so you can still see the actual value for that date) and also include H1.RET as another variable so that it cab be fed into PROC MEANS. A small example of what you want would help (perhaps with 3 or 5 instead of 24 months so that the number of records is smaller).

**data** have ;

do cusip=**1**,**2** ;

rec+**1**;

baseDate = **'01JAN2000'd** ;

do month=**0** to **26** ;

monthDate = intnx('month',baseDate,month);

ret = ranuni(**0**);

output;

end;

end;

**run**;

**proc** **sql** ;

create view roll24 as

select h2.cusip

, h2.monthDate as periodEndDate format=yymmd7.

, h2.ret

, h1.ret as lagret

from have as h1

, have as h2

where h1.cusip=h2.cusip

and intck("MONTH", h1.monthDate, h2.monthDate) between **1** and **24**

group by h2.cusip, h2.monthDate, h2.ret

having count(h2.cusip)=**24**

;

**quit**;

**proc** **means** data=roll24 noprint ;

by cusip periodenddate ret ;

var lagret ;

output out=roll mean=meanRet std=stdRet skew=skewRet ;

**run**;

**proc** **print** data=roll ;

**run**;

period

Obs cusip EndDate ret _TYPE_ _FREQ_ meanRet stdRet skewRet

1 1 2002-01 0.22396 0 24 0.50622 0.29944 -0.26692

2 1 2002-02 0.23832 0 24 0.51477 0.28762 -0.21262

3 1 2002-03 0.64083 0 24 0.49023 0.28492 -0.04201

4 2 2002-01 0.59923 0 24 0.52899 0.28713 0.13578

5 2 2002-02 0.91479 0 24 0.52256 0.28359 0.19230

6 2 2002-03 0.41203 0 24 0.52664 0.28867 0.20478

Solution

03-16-2014
03:55 AM

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03-16-2014 03:55 AM

ZZb is there a reason that you must code in SQL? Do you have a third party DBMS? When you have a third-party DBMS wich one? SQL aggregated functions are as standard as babylonian languages (old tst) for the advanced ones.

I your question the same as: https://communities.sas.com/message/192004

---->-- ja karman --<-----