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Cumulative standard deviation: Difference between revisions
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('std dev = %1' % { sd }) displayNl.</lang>
=={{header|SQL}}==
{{works with|Postgresql}}
<lang SQL>-- the minimal table
create table if not exists teststd (n double precision not null);
-- code modularity with view, we could have used a common table expression instead
create view vteststd as
select count(n) as cnt,
sum(n) as tsum,
sum(power(n,2)) as tsqr
from teststd;
-- you can of course put this code into every query
create or replace function std_dev() returns double precision as $$
select sqrt(tsqr/cnt - (tsum/cnt)^2) from vteststd;
$$ language sql;
-- test data is: 2,4,4,4,5,5,7,9
insert into teststd values (2);
select std_dev() as std_deviation;
insert into teststd values (4);
select std_dev() as std_deviation;
insert into teststd values (4);
select std_dev() as std_deviation;
insert into teststd values (4);
select std_dev() as std_deviation;
insert into teststd values (5);
select std_dev() as std_deviation;
insert into teststd values (5);
select std_dev() as std_deviation;
insert into teststd values (7);
select std_dev() as std_deviation;
insert into teststd values (9);
select std_dev() as std_deviation;
-- cleanup test data
delete from teststd;
</lang>
With a command like '''psql <rosetta-std-dev.sql''' you will get an output like this: (duplicate lines generously deleted, locale is DE)
<pre>
CREATE TABLE
FEHLER: Relation »vteststd« existiert bereits
CREATE FUNCTION
INSERT 0 1
std_deviation
---------------
0
(1 Zeile)
INSERT 0 1
std_deviation
---------------
1
0.942809041582063
0.866025403784439
0.979795897113272
1
1.39970842444753
2
DELETE 8
</pre>
=={{header|Swift}}==
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