I have in front of me a piece of code like this:
FOR row IN 1..l_RowSet(1).count
LOOP
l_a_variable := l_RowSet(1)(row);
END LOOP;
l_RowSet is an ApEx type -- apex_plugin_util.t_column_value_list -- defined thus:
type t_column_value_list is table of wwv_flow_global.vc_arr2 index by pls_integer;
where wwv_flow_global.vc_arr2 is defined as
type vc_arr2 is table of varchar2(32767) index by binary_integer;
The vc_arr2 is passed back to my code from the apex_plugin_util.get_data function. The vc_arr2 is indexed by column number, not by row.
As best I can make out this means that the data is effectively stored in a 2D array, indexed by column and then by row.
When using the LOOP statement, would this be indexed from zero or from one? Because it seems to me that I ought to be able to make that LOOP redundant, ie:
l_a_variable := l_RowSet(1)(1);
But I'd need to know in advance whether to give 0 or 1 as the initial row.
I can't find a clear answer in the Oracle docs (unsurprisingly, "index" is a fairly widely-used term) and a look through SO doesn't show anybody else with the same question either.
An associative array isn't necessarily dense. There may be an element at index 0, there may be an element at index -1, there may be an element at index 1. Or you might have elements at indexes 17, 42, and 127. The code you posted implies that the associative array is dense and that the indexes start at 1.
In the specific case of apex_plugin_util.get_data the collection should be dense and should start at 1. If the loop is actually not doing anything other than what you posted, you could replace it by fetching the last element of l_RowSet(1), i.e.
l_a_variable := l_RowSet(1)(l_RowSet(1).count);
Related
I need to construct a matrix; a number of columns and rows are also in the first row of the matrix, I'll make an example so its more clearer.
4 3
1 2 3
5 6 7
9 10 8
1 11 13
Where m=4 (number of rows) and n=3 (number of columns)
This is an example of a text file. Is something like this even possible?
Program Feb;
const
max=100;
type
Matrix=array[1..max,1..max] of integer;
var datoteka:text;
m,n:integer;
counter:integer;
begin
assign(datoteka,'datoteka.txt');
reset(datoteka);
while not eoln(datoteka) do
begin
read(datoteka, m);
read(datoteka, n);
end;
repeat
read eoln(n)
until eof(datoteka)
write (m,n);
end.
My code isn't a big help, cause I don't know how to write it.
First, have a look at the code I wrote to do the task, and then look at my explanation below.
program Matrixtest;
uses
sysutils;
var
NoOfCols,
NoOfRows : Integer;
Source : TextFile;
Matrix : array of array of integer;
FileName : String;
Row,
Col : Integer; // for-loop iterators to access a single cell of the matrix
Value : Integer;
begin
// First, construct the name of the file defining the matrix
// This assumes that the file is in the same folder as this app
FileName := ExtractFilePath(ParamStr(0)) + 'MatrixDef.Txt';
writeln(FileName); // echo it back to the screen so we can see it
// Next, open the file
Assign(Source, FileName);
Reset(Source);
read(Source, NoOfRows, NoOfCols);
writeln('Cols: ', NoOfCols, 'Rows: ', NoOfRows);
SetLength(Matrix, NoOfCols, NoOfRows);
readln(source); // move to next line in file
// Next, read the array data
for Row := 1 to NoOfRows do begin
for Col := 1 to NoOfCols do begin
read(Source, Value);
Matrix[Col - 1, Row - 1] := Value;
end;
end;
// Display the array contents
for Row := 1 to NoOfRows do begin
for Col := 1 to NoOfCols do begin
writeln('Row: ', Row, ' contents', Matrix[Col - 1, Row - 1]);
end;
end;
Close(Source); // We're done with the file, so close it to release OS resources
readln; // this waits until you press a key, so you can read what's been displayed
end.
In your program, you can use a two-dimensional array to represent your matrix. Free Pascal supports multi-dimensional arrays; see https://wiki.lazarus.freepascal.org/Multidimensional_arrays for more information.
This is a complex task, so it helps to know how to do more basic things like reading an array of a size known at compile-time from a text file.
The wrinkle in this task is that you are supposed to read the dimensions (numbers of rows and columns) of the matrix at run-time from the file which contains the matrix's contents.
One inefficient way to do this would be to declare the matrix array with huge dimensions, larger than anything you would expect in practice, using the type of array declaration in the Wiki page linked above.
A better way is to use dynamic arrays, whose dimensions you can set at run-time. To use this, you need to know:
How to declare a dynamic array in Free Pascal
How to set the dimensions of the array at run-time, once you've picked them up from your matrix-definition file (hint: SetLength is the way to do this)
The fact that a Free Pascal dynamic array is zero-based
The easiest way of managing zero-based arrays is to write your code (in terms of Row and Column variables) as if the matrix were declared as array[1..NoOfRows, 1..NoOfColumns] and subtract one from the array indexes only when you actually access the array, as in:
Row := 3;
Column := 4;
Value := Matrix[Row - 1, Column - 1];
i had a problem when i am using dbms_output package. When i am executing the following code it display integer is 0
declare
v integer;
asq dbms_output.chararr;
begin
dbms_output.put('hi');
dbms_output.put_line('hello!');
asq(1):='sun';
asq(2):='ant';
dbms_output.put_line(asq(1));
dbms_output.put_line(asq(2));
dbms_output.get_lines(asq,v);
dbms_output.put_line('integer is '||v);
end;
but when i am executing the following code i am getting integer is 3
declare
v integer:=5;
asq dbms_output.chararr;
begin
dbms_output.put('hi');
dbms_output.put_line('hello!');
asq(1):='sun';
asq(2):='ant';
dbms_output.put_line(asq(1));
dbms_output.put_line(asq(2));
dbms_output.get_lines(asq,v);
dbms_output.put_line('integer is '||v);
end;
can any one help me why the variation is there in the two procedures
As per documentation, the second parameter to GET_LINES
procedure is IN OUT parameter. It tells the procedure, number of lines to be retrieved from buffer. After the procedure call, it holds number of lines actually retrieved.
In your first example, the value of v is null. So no lines are retrieved and v is assigned the value 0.
In your second example, the value if v is 5. So you are requesting 5 lines, but since there are only three lines(hihello!, sun, ant), three lines are put into array asq and v is assigned 3.
I developed the following sorting algorithm but there are some run time errors that I cant figure out. The program terminates when it comes to the part of filling the array. I'm still a beginner in ada so I couldn't figure out where the problem is...
With Ada.Text_IO;
With Ada.Integer_Text_IO;
Use Ada.Integer_Text_IO;
Use Ada.Text_IO;
Procedure sort is
n,i,x : Integer;
-- Max_Heapify Function...
Procedure Max_Heapify ( i, n : integer) is
j, Temp : Integer;
begin
Temp:=Int_Acc(i);
j:=2*i;
if Temp>Int_Acc(j) then
elsif Temp<=Int_Acc(j) then
Int_Acc(j/2):=Int_Acc(j);
j:=2*j;
end if;
end loop;
Int_Acc(j/2):=Temp;
end Max_Heapify;
begin
Get(n);
for i in MyArr'range loop
Put_Line("Enter Element " & Integer'Image(i));
Get(MyArr(i));
end loop;
end;
end sort;
Thanks in advance :)
Your Problem is that you are insisting on writing Ada code using c - Style programming paradigms.
Firstly:
The declarations:
Type Arr is array(1..20) of Integer;
Type int_access is access Arr;
MyArr : int_access;
Where you use Int_Acc : in out int_access as parameters to procedures are useless in Ada. You are trying to pass a pointer to an array in (which you are doing!), but you should just pass your Type Arr as in out - The Ada compiler knows to do this as a pointer!
Secondly:
I cannot see where you actually allocate any memory to MyArr. This is a possible source of your runtime error. (when you write to or index an array that does not exist, i would expect to have a problem!)
Thirdly:
You seem to be mixing fixed length arrays with variable length input. If N > 20, you will have a problem.
Fourthly:
Insulting the language is not the best way of getting help from those who like it.
NWS has nailed it : there is a pointer, but no array there.
But it's clear that you have learned C, which leaves you with a lot to learn about other languages including Ada. There really are better ways of doing many things, that aren't taught to C programmers because C doesn't allow them.
Allocating variable sized arrays without pointers, malloc and free for example...
Type Arr is array(positive range <>) of Integer; -- of any size
begin
Put_Line("Enter Number Of Elements Of Array");
Get(n);
declare -- now we know the size
My_Arr : Arr(1 .. n);
begin -- My_Arr is in scope until the end of this block
...
end;
end sort;
Using the type system better...
Bad programming :
for i in 1 .. n loop
Get(MyArr(i));
end loop;
HeapSort(MyArr,n);
for i in 1 .. n loop
Put_Line(Integer'Image(MyArr(i)));
end loop;
This is bad because it violates the DRY principle : loop bounds repeated, and something that hopefully represents the array size passed around as a separate parameter... a maintenance nightmare if you decide to rename n to something meaningful for example.
better programming : Use the type system. Recognise that merely declaring an array has declared a new subtype of integer, representing the index of the array. You can access it as My_Arr'range, and the high bound as My_Arr'last.
for i in My_Arr'range loop
Get(MyArr(i));
end loop;
HeapSort(MyArr);
for i in My_Arr'range loop
Put_Line(Integer'Image(MyArr(i)));
end loop;
And accidents such as redefining n after the array declaration can no longer generate buffer overflows.
NOTE: Heapsort now gets its range from the array. (Max_Heapify may still need a separate parameter to operate on subsets of the array)
Arguably best - if it makes the intent clearer - name the index datatype explicitly and use it...
declare -- now we know the size
subtype My_Range is positive range 1 .. n;
My_Arr : Arr(My_Range);
begin -- My_Arr is in scope until the end of this block
for i in My_Range loop ...
And lastly, which do you prefer; a Storage_Error exception immediately the bug occurs (writing to memory you forgot to allocate) or something odd happening much later because something scribbled across another variable?
EDIT
Having cleared up the major issues two more subtle ones remain...
If I compile the modified program (in Gnat 4.8) I get several warnings : one of them is important and tells you exactly what the problem is...
Most of the warnings stem from the fact that
for i in My_Arr'range loop
declares its own loop variable i which hides any existing in-scope declaration. So you can tidy up the code by removing the unnecessary declarations.
What remains is:
sort.adb:51:28: warning: loop range may be null
sort.adb:51:28: warning: bounds may be wrong way round
The for loop bounds are empty ranges, reversed...
1 .. 3 declares a subtype with 3 values
reverse 1 .. 3 declares the same subtype and iterates backwards over it.
But 3 .. 1 declares an EMPTY subtype (containing NO valid values) so iterating over it - either way round - does precisely nothing.
Hopefully that is the missing part of the puzzle. I'm not clear why one faulty loop gets this warning while the other (at line 38) doesn't...
if j<n **and then** Int_Acc(j+1)>Int_Acc(j) then
j:=j+1;
I think you want just 'and' instead of 'and then,' although I haven't looked at Ada code in years.
Did that compile?
I have a 250*2001 matrix. I want to find the location for the maximum value for a(:,i) where i takes 5 different values: i = i + 256
a(:,256)
a(:,512)
a(:,768)
a(:,1024)
a(:,1280)
I tried using MAXLOC, but since I'm new to fortran, I couldn't get it right.
Try this
maxloc(a(:,256:1280:256))
but be warned, this call will return a value in the range 1..5 for the second dimension. The call will return the index of the maxloc in the 2001*5 array section that you pass to it. So to get the column index of the location in the original array you'll have to do some multiplication. And note that since the argument in the call to maxloc is a rank-2 array section the call will return a 2-element vector.
Your question is a little unclear: it could be either of two things you want.
One value for the maximum over the entire 250-by-5 subarray;
One value for the maximum in each of the 5 250-by-1 subarrays.
Your comments suggest you want the latter, and there is already an answer for the former.
So, in case it is the latter:
b(1:5) = MAXLOC(a(:,256:1280:256), DIM=1)
In HASH JOIN method of oracle, HASH TABLE will be built on one of the tables and other will be joined depending on the values in the hash table.
Could you please let me know what is Hash table? What is the structure of hash table? how will it be created?
A hash table is a table where you can store stuff by the use of a key. It is like an array but stores things differently
a('CanBeVarchar') := 1; -- A hash table
In oracle, they are called associative arrays or index by tables. and you make one like this:
TYPE aHashTable IS TABLE OF [number|varchar2|user-defined-types] INDEX BY VARCHAR2(30);
myTable aHashTable;
So, what is it? it's just a bunch of key-value pairs. The data is stored as a linked list with head nodes that group the data by the use of something called HashCode to find things faster. Something like this:
a -> b -> c
Any Bitter Class
Array Bold Count
Say you are storing random words and it's meaning (a dictionary); when you store a word that begins with a, it is stored in the 'a' group. So, say you want this myTable('Albatroz') := 'It's a bird', the hash code will be calculated and put in the A head node, where it belongs: just above the 'Any'. a, has a link to Any, which has a link to Array and so on.
Now, the cool thing about it is that you get fast data retreival, say you want the meaning of Count, you do this definition := myTable('Count'); It will ignore searching for Any, Array, Bitter, Bold. Will search directly in the C head node, going trhough Class and finally Count; that is fast!
Here a wikipedia Link: http://en.wikipedia.org/wiki/Hash_table
Note that my example is oversimplified read with a little bit of more detail in the link.
Read more details like the load factor: What happens if i get a LOT of elements in the a group and few in the b and c; now searching for a word that begins with a is not very optinmal, is it? the hash table uses the load factor to reorganize and distribute the load of each node, for example, the table can be converted to subgroups:
From this
a b -> c
Any Bitter Class
Anode Bold Count
Anti
Array
Arrays
Arrow
To this
an -> ar b -> c
Any Array Bitter Class
Anode Arrays Bold Count
Anti Arrow
Now looking for words like Arrow will be faster.