replacing values of specific index in postgresql 9.3 - postgresql

Question

CREATE OR REPLACE FUNCTION array_replace(INT[]) RETURNS float[] AS $$
DECLARE
arrFloats ALIAS FOR $1;
J int=0;
x int[]=ARRAY[2,4];
-- xx float[]=ARRAY[2.22,4.33];
b float=2.22;
c float=3.33;
retVal float[];
BEGIN
FOR I IN array_lower(arrFloats, 1)..array_upper(arrFloats, 1) LOOP
FOR K IN array_lower(x, 1)..array_upper(x, 1) LOOP
IF (arrFloats[I]= x[K])THEN
retVal[j] :=b;
j:=j+1;
retVal[j] :=c;
j:=j+1;
ELSE
retVal[j] := arrFloats[I];
j:=j+1;
END IF;
END LOOP;
END LOOP;
RETURN retVal;
END;
$$ LANGUAGE plpgsql STABLE RETURNS NULL ON NULL INPUT;
When I run this query
SELECT array_replace(array[1,20,2,5]);
it give me output like this
"[0:8]={1,1,20,20,2.22,3.33,2,5,5}"
Now I do not know why it is coming this duplicate values. I mean it is straight away a nested loop ...
I need a output like this one
"[0:8]={1,20,2.22,3.33,5}"

Answer 1

You have a double loop with the x array having two elements. On every iteration you push elements onto the result array, hence you get twice as many values.
If I understand you logic correctly, you want to scan the input array for values of another array in that same order. If the same, then replace these values with another array, leaving other values intact. There are no built-in functions to help you here, so you have to do this from scratch:
CREATE FUNCTION array_replace(arrFloats float[]) RETURNS float[] AS $$
DECLARE
searchArr float[] := ARRAY[1.,20.];
replaceArr float[] := ARRAY[1.11,1.,111.,20.2,20.222];
retVal float[];
i int;
ndx int;
len int;
upp int;
low int
BEGIN
low := array_lower(searchArr, 1)
upp := array_upper(searchArr, 1);
len := upp - low + 1;
i := array_lower(arrFloats, 1);
WHILE i <= array_upper(arrFloats, 1) LOOP -- Use WHILE LOOP so can update i
ndx := i; -- index into arrFloats for inner loop
FOR j IN low .. upp LOOP
IF arrFloats[ndx] != searchArr[j] THEN
-- No match so put current element of arrFloats in the result and update i
retVal := retVal || arrFloats[i];
i := i + 1;
EXIT; -- No need to look further, break out of inner loop
END IF;
ndx := ndx + 1;
IF j = upp THEN
-- We have a match so append the replaceArr to retVal and
-- increase i by length of search_array
retVal := retVal || replaceArr;
i := i + len;
END IF;
END LOOP;
END LOOP;
RETURN retVal;
END;
$$ LANGUAGE plpgsql STABLE STRICT;
This function would become much more flexible if you made searchArr and replaceArr into parameters as well.
Test
patrick#puny:~$ psql -d test
psql (9.5.0, server 9.4.5)
Type "help" for help.
test=# select array_replace(array[1,20,2,5]);
array_replace
------------------------------
{1.11,1,111,20.2,20.222,2,5}
(1 row)
test=# select array_replace(array[1,20,2,5,1,20.1,1,20]);
array_replace
------------------------------------------------------------
{1.11,1,111,20.2,20.222,2,5,1,20.1,1.11,1,111,20.2,20.222}
(1 row)
As you can see it works for multiple occurrences of the search array.