Is there any way to convert Postgres PATH type to an ARRAY in order to have index access to it's points?
There is no way to do that with PostgreSQL alone - you'd have to write your own C function.
With the PostGIS extension, you can cast the path to geometry and perform the operation there:
SELECT array_agg(CAST(geom AS point))
FROM st_dumppoints(CAST(some_path AS geometry));
Try a variant of this..
CREATE OR REPLACE FUNCTION YADAMU.YADAMU_make_closed(point[])
returns point[]
STABLE RETURNS NULL ON NULL INPUT
as
$$
select case
when $1[1]::varchar = $1[array_length($1,1)]::varchar then
$1
else
array_append($1,$1[1])
end
$$
LANGUAGE SQL;
--
CREATE OR REPLACE FUNCTION YADAMU.YADAMU_AsPointArray(path)
returns point[]
STABLE RETURNS NULL ON NULL INPUT
as
$$
--
-- Array of Points from Path
--
select case
when isClosed($1) then
YADAMU.YADAMU_make_closed(array_agg(point(v)))
else
array_agg(point(v))
end
from unnest(string_to_array(left(right($1::VARCHAR,-2),-2),'),(')) v
$$
LANGUAGE SQL;
--
Eg
yadamu=# select * from unnest(YADAMU.YADAMU_asPointArray(Path '((0,1),(1,0),(4,0))'));
unnest
--------
(0,1)
(1,0)
(4,0)
(3 rows)
Related
I have a number in binary (base-2) representation:
"10100110"
How can I transform it to a number in Snowflake?
Snowflake does not provide number or Integer to Binary function out of the box, however these UDF function can be used instead
I also overloaded the UDF in the event a string gets passed.
CREATE OR REPLACE FUNCTION int_to_binary(NUM VARIANT)
RETURNS string
LANGUAGE JAVASCRIPT
AS $$
return (NUM >>> 0).toString(2);
$$;
CREATE OR REPLACE FUNCTION int_to_binary(NUM STRING)
RETURNS string
LANGUAGE JAVASCRIPT
AS $$
return (NUM >>> 0).toString(2);
$$;
I tried with a SQL pure UDF - it worked at first, but not when using it with data over a table.
So I had to create a Javascript UDF:
create or replace function bin_str_to_number(a string)
returns float
language javascript
as
$$
return parseInt(A, 2)
$$
;
select bin_str_to_number('110');
For the record, this is the error I got when attempting a pure SQL UDF for the same:
SQL compilation error: Unsupported subquery type cannot be evaluated
The UDF:
create or replace function bin_str_to_number(a string)
returns number
as
$$
(select sum(value::number*pow(2,index))::number
from table(flatten(input=>split_string_to_char(reverse(a)))))
$$
That was a fun challenge for this morning! If you want to do it in pure SQL:
with binary_numbers as (
select column1 as binary_string
from (values('10100110'), ('101101101'), ('1010011010'), ('1011110')) tab
)
select
binary_string,
sum(to_number(tab.value) * pow(2, (tab.index - 1))) decimal_number
from
binary_numbers,
table(split_to_table(trim(replace(replace(reverse(binary_numbers.binary_string), '1', '1,'), '0', '0,' ), ','), ',')) tab
group by binary_string
Produces:
BINARY_STRING
DECIMAL_NUMBER
10100110
166
101101101
365
1010011010
666
1011110
94
I'm using PostgreSQL 9.3.
The table partner.partner_statistic contains the following columns:
id reg_count
serial integer
I wrote the function convert(integer):
CREATE FUNCTION convert(d integer) RETURNS integer AS $$
BEGIN
--Do something and return integer result
END
$$ LANGUAGE plpgsql;
And now I need to write a function returned array of integers as follows:
CREATE FUNCTION res() RETURNS integer[] AS $$
<< outerblock >>
DECLARE
arr integer[]; --That array of integers I need to fill in depends on the result of query
r partner.partner_statistic%rowtype;
table_name varchar DEFAULT 'partner.partner_statistic';
BEGIN
FOR r IN
SELECT * FROM partner.partner_statistic offset 0 limit 100
LOOP
--
-- I need to add convert(r[reg_count]) to arr where r[id] = 0 (mod 5)
--
-- How can I do that?
END LOOP;
RETURN;
END;
$$ LANGUAGE plpgsql;
You don't need (and shouldn't use) PL/PgSQL loops for this. Just use an aggregate. I'm kind of guessing about what you mean by "where r[id] = 0 (mod 5) but I'm assuming you mean "where id is evenly divisible by 5". (Note that this is NOT the same thing as "every fifth row" because generated IDs have gaps).
Something like:
SELECT array_agg(r.reg_count)
FROM partner.partner_statistic
WHERE id % 5 = 0
LIMIT 100
probably meets your needs.
If you want to return the value, use RETURN QUERY SELECT ... or preferably use a simple sql language function.
If you want a dynamic table name, use:
RETURN QUERY EXECUTE format('
SELECT array_agg(r.reg_count)
FROM %I
WHERE id % 5 = 0
LIMIT 100', table_name::regclass);
I need to convert from an array to rows and back to an array for filtering records.
I'm using information_schema._pg_expandarray in a SELECT query to get one row per value in the array.
Given the following array :
"char"[]
{i,i,o,t,b}
_pg_expandarray retuns 5 rows with 1 column of type record :
record
(i,1)
(i,2)
(o,3)
(t,4) <= to be filtered out later
(b,5)
I need to filter this result set to exclude record(s) that contains 't'.
How can I do that ? Should I convert back to an array ?
Is there a way to filter on the array directly ?
Thanks in advance.
If your objective is to produce a set of rows as above but with the row containing 't' removed, then this does the trick:
test=> select *
from information_schema._pg_expandarray(array['i','i','o','t','b']) as a(i)
where a.i!='t';
i | n
---+---
i | 1
i | 2
o | 3
b | 5
(4 rows)
As an aside, unless you particularly want the index returned as a second column, I'd be inclined to use unnest() over information_schema._pg_expandarray(), which does not appear to be documented and judging by the leading '_' in the name is probably intended for internal usage.
There does not seem to be any built in function to filter arrays. Your question implies you may want the result in array form - if that is the case then writing a simple function is trivial. Here is an example:
CREATE OR REPLACE FUNCTION array_filter(anyarray, anyelement) RETURNS anyarray
AS $$
DECLARE
inArray ALIAS FOR $1;
filtValue ALIAS FOR $2;
outArray ALIAS FOR $0;
outIndex int=0;
BEGIN
FOR I IN array_lower(inArray, 1)..array_upper(inArray, 1) LOOP
IF inArray[I] != filtValue THEN
outArray[outIndex] := inArray[I];
outIndex=outIndex+1;
END IF;
END LOOP;
RETURN outArray;
END;
$$ LANGUAGE plpgsql
STABLE
RETURNS NULL ON NULL INPUT;
Usage:
test=> select array_filter(array['i','i','o','t','b'],'t');
array_filter
-----------------
[0:3]={i,i,o,b}
(1 row)
This question already has answers here:
Postgres function returning table not returning data in columns
(2 answers)
Closed 8 years ago.
I created function like below:
CREATE TYPE points AS (
"gid" double precision
, "elevation" double precision
, "distance" double precision
, "x" double precision
, "y" double precision
);
CREATE OR REPLACE FUNCTION public.nd_test4()
RETURNS SETOF points AS $$
DECLARE
sql text;
rec points;
BEGIN
sql := 'select
"gid"
, "elev" as "elevation"
, st_distance(ST_MakePoint(1093147, 1905632) , "the_geom" ) as "distance"
, st_x("the_geom") as "x"
, st_y("the_geom")as "y"
from
"elevation-test"
where
st_within("the_geom" ,st_buffer(ST_MakePoint(1093147, 1905632), 15) )
order by distance limit 4';
FOR rec IN EXECUTE(sql) LOOP
RETURN NEXT rec;
END LOOP;
END;
$$ LANGUAGE plpgsql VOLATILE;
And when I run the function like select nd_test4();, I get a result with no filed names like below.
image?
How can I get result with filed name like this:
gid | elevation | distance | x | y
----+-----------+----------+---------+-------
1 | 350.0 | 10 | 12345.1 | 12435
Call the function with:
SELECT * FROM nd_test4();
Also, your function definition is needlessly convoluted. Simplify to:
CREATE OR REPLACE FUNCTION public.nd_test4()
RETURNS SETOF points AS
$func$
BEGIN
RETURN QUERY
SELECT gid
,elev -- AS elevation
,st_distance(ST_MakePoint(1093147, 1905632) , the_geom ) -- AS distance
,st_x(the_geom) -- AS x
,st_y(the_geom) -- AS y
FROM "elevation-test"
WHERE st_within(the_geom, st_buffer(ST_MakePoint(1093147, 1905632), 15))
ORDER BY distance
LIMIT 4;
END
$func$ LANGUAGE plpgsql;
Or better yet, use a plain SQL function here:
CREATE OR REPLACE FUNCTION public.nd_test4()
RETURNS SETOF points AS
$func$
SELECT gid
,elev -- AS elevation
,st_distance(ST_MakePoint(1093147, 1905632) , the_geom ) -- AS distance
,st_x(the_geom) -- AS x
,st_y(the_geom) -- AS y
FROM "elevation-test"
WHERE st_within(the_geom, st_buffer(ST_MakePoint(1093147, 1905632), 15))
ORDER BY distance
LIMIT 4
$func$ LANGUAGE sql;
No need for dynamic SQL.
I also stripped the gratuitous double quotes. Not needed for legal, lower-case identifiers. Exception is "elevation-test". You shouldn't use an operator (-) as part of a table name. That's just begging for trouble.
Aliases in the function body are replaced by column names of the composite type. They are only visible inside the function and therefore just documentation in your case.
I'm trying to implement an exponential moving average (EMA) on postgres, but as I check documentation and think about it the more I try the more confused I am.
The formula for EMA(x) is:
EMA(x1) = x1
EMA(xn) = α * xn + (1 - α) * EMA(xn-1)
It seems to be perfect for an aggregator, keeping the result of the last calculated element is exactly what has to be done here. However an aggregator produces one single result (as reduce, or fold) and here we need a list (a column) of results (as map). I have been checking how procedures and functions work, but AFAIK they produce one single output, not a column. I have seen plenty of procedures and functions, but I can't really figure out how does this interact with relational algebra, especially when doing something like this, an EMA.
I did not have luck searching the Internets so far. But the definition for an EMA is quite simple, I hope it is possible to translate this definition into something that works in postgres and is simple and efficient, because moving to NoSQL is going to be excessive in my context.
Thank you.
PD: here you can see an example:
https://docs.google.com/spreadsheet/ccc?key=0AvfclSzBscS6dDJCNWlrT3NYdDJxbkh3cGJ2S2V0cVE
You can define your own aggregate function and then use it with a window specification to get the aggregate output at each stage rather than a single value.
So an aggregate is a piece of state, and a transform function to modify that state for each row, and optionally a finalising function to convert the state to an output value. For a simple case like this, just a transform function should be sufficient.
create function ema_func(numeric, numeric) returns numeric
language plpgsql as $$
declare
alpha numeric := 0.5;
begin
-- uncomment the following line to see what the parameters mean
-- raise info 'ema_func: % %', $1, $2;
return case
when $1 is null then $2
else alpha * $2 + (1 - alpha) * $1
end;
end
$$;
create aggregate ema(basetype = numeric, sfunc = ema_func, stype = numeric);
which gives me:
steve#steve#[local] =# select x, ema(x, 0.1) over(w), ema(x, 0.2) over(w) from data window w as (order by n asc) limit 5;
x | ema | ema
-----------+---------------+---------------
44.988564 | 44.988564 | 44.988564
39.5634 | 44.4460476 | 43.9035312
38.605724 | 43.86201524 | 42.84396976
38.209646 | 43.296778316 | 41.917105008
44.541264 | 43.4212268844 | 42.4419368064
These numbers seem to match up to the spreadsheet you added to the question.
Also, you can define the function to pass alpha as a parameter from the statement:
create or replace function ema_func(state numeric, inval numeric, alpha numeric)
returns numeric
language plpgsql as $$
begin
return case
when state is null then inval
else alpha * inval + (1-alpha) * state
end;
end
$$;
create aggregate ema(numeric, numeric) (sfunc = ema_func, stype = numeric);
select x, ema(x, 0.5 /* alpha */) over (order by n asc) from data
Also, this function is actually so simple that it doesn't need to be in plpgsql at all, but can be just a sql function, although you can't refer to parameters by name in one of those:
create or replace function ema_func(state numeric, inval numeric, alpha numeric)
returns numeric
language sql as $$
select case
when $1 is null then $2
else $3 * $2 + (1-$3) * $1
end
$$;
This type of query can be solved with a recursive CTE - try:
with recursive cte as (
select n, x ema from my_table where n = 1
union all
select m.n, alpha * m.x + (1 - alpha) * cte.ema
from cte
join my_table m on cte.n = m.n - 1
cross join (select ? alpha) a)
select * from cte;
--$1 Stock code
--$2 exponential;
create or replace function fn_ema(text,numeric)
returns numeric as
$body$
declare
alpha numeric := 0.5;
var_r record;
result numeric:=0;
n int;
p1 numeric;
begin
alpha=2/(1+$2);
n=0;
for var_r in(select *
from stock_old_invest
where code=$1 order by stock_time desc)
loop
if n>0 then
result=result+(1-alpha)^n*var_r.price_now;
else
p1=var_r.price_now;
end if;
n=n+1;
end loop;
result=alpha*(result+p1);
return result;
end
$body$
language plpgsql volatile
cost 100;
alter function fn_ema(text,numeric)
owner to postgres;