Date: Wed, 31 Jan 2007 18:31:18 -0500
Reply-To: Arthur Tabachneck <art297@NETSCAPE.NET>
Sender: "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From: Arthur Tabachneck <art297@NETSCAPE.NET>
Subject: Re: OT: Chance to Make SAS-L History: Did You Know That...
David,
I'm answering your question via the "Did you know that" thread, because it
reminded me of a thread a couple of years ago that is well worth repeating.
Did you know that: When running a proc sort on a data file that already
has a sortedby flag set for the sort order of interest, the sort won't
work unless you include the FORCE option?
The thread where this was discussed can be found at:
http://xrl.us/ukeu
Art
---------
On Thu, 1 Feb 2007 09:44:30 +1100, Johnson, David
<David.Johnson@CBA.COM.AU> wrote:
>Time for a different soapbox...
>
>A colleague in the Apple wanted a large amount of data that took some
>hours to prepare for transmission.
>
>In preparing the tables, I used the SortedBy flag to identify the data
>order and simplify reconstruction and indexing.
>
>For my 2 / 100 of local currency: where the data is ordered (and I use
>that term deliberately), it makes sense to specify on the SAS table
>header that it is "SortedBy". As previously remarked, a sort procedure
>is skipped if the data is expected to be in the correct order.
>
>It is also worth noting that if the flag is incorrectly set and an index
>is requested on the table, then SAS produces a very helpful message when
>it aborts indexing to state that the table is not in the "order... as
>asserted".
>
>It is perhaps unfortunate that the DataSets procedure that attempts to
>modify the table and apply the index doesn't remove the SortedBy flag
>when the data order is found to differ from the flag assertion. Might
>that be a SAS ballot opportunity for the future?
>
>Kind regards
>
>David
>
>
>-----Original Message-----
>From: SAS(r) Discussion [mailto:SAS-L@LISTSERV.UGA.EDU] On Behalf Of Lou
>Sent: Wednesday, 31 January 2007 1:04 PM
>To: SAS-L@LISTSERV.UGA.EDU
>Subject: Re: Sorted Columns
>
>"Deep" <ADSingh78@GMAIL.COM> wrote in message
>news:200701301956.l0UJ4b3h011199@mailgw.cc.uga.edu...
>> What is the best way to know that the dataset is sorted using which
>> variable names. I tried the following but did not help. I am using SAS
>v8.
>>
>> proc sql;
>> create table test as
>> select *
>> from dictionary.columns
>> where libname='WORK' and memname='MYDATA';
>> quit;
>>
>> Please advise.
>
>The dataset header maintains a flag called (if I remember rightly)
>SORTEDBY.
>You can read the contents of that flag with PROC CONTENTS, by accessing
>the dictionary tables using PROC SQL, or using the dictionary views in a
>DATA or PROC step.
>
>However, it won't tell you if the dataset is in sorted order "by
>construction". For instance, the data step
>
>DATA FEE;
> DO N = 1 TO 10;
> OUTPUT;
> END;
> STOP;
>RUN;
>
>produces a dataset that is in the same order as it would be if it had
>been sorted on variable N by PROC SORT, but the sorted by flag is blank.
>
>Further, you can change the value of the flag without sorting the
>dataset - if you're feeling particularly malicious, you can set the flag
>to say the data set is sorted by some variable(s) when in fact it is
>not.
>
>The "best" way to know a dataset is sorted by some list of variable
>names is to sort it just before you're going to use it.
>
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