I am getting a rather strange behaviour when invoking oracle instr function, or probably I'm blind enough not to see my stupid mistake.
Actually I written a procedure to split a string. For example if we have string
a,e,i,o,u
then my split method will look like
string_split('a,e,i,o,u',',',5);
where first parameter is the string to split while second one is the separator and third one is the number of element I know is there after splitting.
Now, of number of things , one thing my procedure do is invoke
start_index := instr(temp_string_to_split,',',1,(total_element-i));
But the moment it is invoked I get a
ORA-06512 ,numeric or value error
But if I invoke
start_index := instr(temp_string_to_split,1,(total_element-i));
the procedure runs,though not in a desirable manner. Note that in second invocation separator parameter is missing, and directly number is passed as the second parameter, which I guess should have cause big time exception. But surprisingly it goes and run fine.
Can somebody explain this anomaly...or help me see if I'm missing something.
Thanks,
Mawia
I'm assuming that in your call to instr, temp_string_to_split is the string that was passed to string_split, and (total_element-i) is meant to be an iterator over the number of splits to make. (As an aside, it seems odd that you have ',' hardcoded in this call, when you appear to be passing it as a parameter to string_split.
I tried emulating this with the following SQL, which worked fine:
SELECT LEVEL,instr('a,e,i,o,u',',',1,LEVEL)
from dual connect by level < 5;
Do you know the exact values of temp_string_to_split, total_element, and i on the call to instr that caused the error?
Thanks a lot all for responding.
Actually as I told earlier, I was calling
start_index := instr(temp_string_to_split,',',1,(total_element-i));
in a loop. Now as a final value of the loop
(total_element-i)
was getting negative. And this was the root of malady.
One thing, I'm still puzzled though is as it was a run time generated condition, that is to say everything before the final invocation was legal. Then why I dont see on console the result of few of DBMS_OUTPUT.PUT_LINE statement which I had put into to trace the execution.
Thanks,
Mawia
Related
I'm looking for some help understanding why I get an error (no implicit conversion of nil into String) when attempting to use a for-loop to search through an array of letters (and add them to a resulting string, which seems to be the real problem), but not when I use a while-loop or 'each' for the same purposes. I've looked through a lot of documentation, but haven't been able to find an answer as to why this is happening. I understand that I could just use the "each" method and call it a day, but I'd prefer to comprehend the cause as well as the effect (and hopefully avoid this problem in the future).
The following method works as desired: printing "result" which is the original string, only with "!" in place of any vowels.
s="helloHELLO"
result=""
vowels=["a","e","i","o","u","A","E","I","O","U"]
string_array=s.split("")
string_array.each do |i|
if vowels.include?(i)
result+="!"
else
result+=i
end
end
puts result
However, my initial attempt (posted below) raises the error mentioned above: "no implicit conversion of nil into String" citing lines 5 and 9.
s="helloHELLO"
result=""
vowels=["a","e","i","o","u","A","E","I","O","U"]
string_array=s.split("")
for i in 0..string_array.length
if vowels.include?(string_array[i])
result+= "!"
else
result+=string_array[i]
end
end
puts result
Through experimentation, I managed to get it working; and I determined--through printing to screen rather than storing in "result"--that the problem occurs during concatenation of the target letter to the string "result". But why is "string_array[i]" (line #9) seen as NIL rather than as a String? I feel like I'm missing something very obvious.
If it matters: This is just a kata on CodeWars that lead me to a fundamental question about data types and the mechanics of the for..in loop. This seemed very relevant, but not 100% on the mark for my question: "for" vs "each" in Ruby.
Thanks in advance for the help.
EDIT:
Okay, I think I figured it out. I'd still love some answers though, to confirm, clarify, or downright refute.
I realized that if I wanted to use the for-loop, I should use the array itself as the "range" rather than "0..array.length", like so:
s="helloHELLO"
result=""
vowels=["a","e","i","o","u","A","E","I","O","U"]
string_array=s.split("")
for i in string_array
if vowels.include?(i)
result+= "!"
else
result+=i
end
end
puts result
So, is it that since the "each" method variable (in this case, "i") doesn't exist outside the scope of the main block, its datatype become nil after evaluating whether it's included in the 'vowels' array?
You got beaten by the classical error when iterating an array starting with index 0, instead of length as end position it should be length-1.
But it seems like you come from some other programming language, your code is not Rubyesque, a 'For' for example is seldom used.
Ruby is a higher language than most others, it has many solutions build in, we call it 'sugared' because Ruby is meant to make us programmers happy. What you try to achieve can be done in just one line.
"helloHELLO".scan(/[aeoui]/i).count
Some explanation: the literal array "hello HELLO" is a String, meaning an object of the String class and as such has a lot of methods you can use, like scan, which scans the string for the regular expression /[aeoui]/ which means any of the characters enclosed in the [], the i at the end makes it case insentitive so you don't have to add AEOUI. The scan returns an array with the matching characters, an object of the Array class has the method count, which gives us the ... Yeah once you get the drift it's easy, you can string together methods which act upon each other.
Your for loop:
for i in 0..string_array.length
loops from 0 to 10.
But string[10] #=> nil because there is no element at index 10. And then on line 9 you try to add nil to result
result = result + string_array[i] #expanded
You can't add nil to a string like this, you have to convert nil to a string explicitly thus the error. The best way to fix this issue is to change your for loop to:
for i in 0..string_array.length-1
Then your loop will finish at the last element, string[9].
This is a basic question on the use of Trace Tables to assist in a dry run of a simple algorithm.
What I find most tricky is when to take a new line in the trace table? For example, take the following question:
Here is the array of integers which it applies to:
The following trace table is presented as one completes a dry run. Here is the solution:
I understand that initialising the variables Number, Lower & Upper appear on the first line, but when I go into the While Loop, I am tempted to put the value 5 on the first line also, for the variable Current. In essence, this is what I am tempted to do:
Why does this solution require that the value for Current, which is 5, appear on the second line? I suppose the question could be rephrased to 'When do I take a new line in a trace table?'
Thanks.
I think there is no specific way to do trace table, which means you have to setup your rules before you work and go on.
consider this example:
and this also:
did you notice the difference between loop iterator in each one. In first example they put the initialization value of the iterator in first line, and in second example they put the initialization of the loop iterator in the second line.
also have a look at wiki they also put the loop initialization in the second line.
also this video has similar example to those I posted here and is always start loop iterator in the second line.
also this example has totally different approach, which is each line of code in a new line in the trace table.
you can find also another different approach for trace table here
Finally:
In my opinion chose the rules that make sense for you, for example:
1-first line will contain the default values for the variables.
2-regarding loop iterations, put loop iterator in the same line as the variables that affected by this iteration, like the second example I posted above.
regarding your question I think it's more clear to put Current first value 5 in the second line, so you can track what each loop iteration affect your variables in a clear way.
It has been a while since I've used Mathematica, and I looked all throughout the help menu. I think one problem I'm having is that I do not know what exactly to look up. I have a block of code, with things like appending lists and doing basic math, that I want to define as a single variable.
My goal is to loop through a sequence and when needed I wanted to call a block of code that I will be using several times throughout the loop. I am guessing I should just put it all in a loop anyway, but I would like to be able to define it all as one function.
It seems like this should be an easy and straightforward procedure. Am I missing something simple?
This is the basic format for a function definition in Mathematica.
myFunc[par1_,par2_]:=Module[{localVar1,localVar2},
statement1; statement2; returnStatement ]
Your question is not entirely clear, but I interpret that you want something like this:
facRand[] :=
({b, x} = Last#FactorInteger[RandomInteger[1*^12]]; Print[b])
Now every time facRand[] is called a new random integer is factored, global variables b and x are assigned, and the value of b is printed. This could also be done with Function:
Clear[facRand]
facRand =
({b, x} = Last#FactorInteger[RandomInteger[1*^12]]; Print[b]) &
This is also called with facRand[]. This form is standard, and allows addressing or passing the symbol facRand without triggering evaluation.
I have been working on a code in prolog for a while now and it is near compiling worthy and all my ideas seem to be solid so it should work when it compiles. It is a program that consults a database file for a list of clauses and then it awaits for a query by the user which it will then pick what information it needs from the sentence and query the database appropriately but there is a block of code that keeps giving me errors complaining that the flowpattern doesn't exist in the standard predicate this may be a silly question but even with all the looking into this I have done i can't find out how to fix this problem if someone could help me out or point me in the right direction that would be greatly appreciated.
Here is the block of code that gives the error:
loop(STR):-
scan(STR,LIST),
filter(LIST,LISroT1),
pars(LIST1,LIST2),
fail.
loop(STR):- STR >< "",readquery(L),loop(L).
readquery(QUERY):-nl,nl,write("Query: "),readln(QUERY).
scan(STR,[TOK|LIST]):-
fronttoken(STR,SYMB,STR1),!,
upper_lower(SYMB,TOK),
scan(STR1,LIST).
the specific line that the compiler complains about is fronttoken(STR,SYMB,STR),!,
any help will be apreaciated thanks!
Since we are looking at an "ex[c]er[p]t" of the code, it's hard to be sure what is going wrong, but the the given evidence points to this: loop/1 is being called before readquery/1 can do its work to populate (bind) the argument STR to loop/1.
Notice that loop/1 calls itself (recursively), and does so in a repeat/fail pattern. But the first time loop/1 runs, there's no indication in the code shown of how argument STR would get populated.
A clearer (more self-contained) code snippet would be like this:
loop :-
readquery(STR),
scan(STR,LIST),
filter(LIST,LISroT1),
pars(LIST1,LIST2),
fail.
loop :- loop.
This makes it clear that predicate loop doesn't actually return any result (and the given code snippet isn't complete enough to make clear what the program as a whole accomplishes). It assumes that the clauses ahead of fail in loop are deterministic, so that in failing, control passes through to the second (recursive) clause of loop/0. If this is not the case, the determinism could be forced by wrapping each call inside once/1.
I've got a quick question about default values in PL/SQL functions in Oracle. Take this program as an example;
create or replace
FUNCTION testFunction
(
varNumber IN NUMBER DEFAULT 0
)
RETURN NUMBER
AS
BEGIN
dbms_output.put_line(varNumber);
RETURN varNumber;
END;
The idea here being that if no value is specified for varNumber when this function is called, then it will take the value of 0.
Now, my problem is that my functions are getting called from a web services layer that will always pass in NULL as the value for parameters which it doesn't have a value for. Oracle interprets NULL as a value, and so does not initialise varNumber to its default of 0.
I can see why this approach makes sense, but I was wondering if there was a way to override this behaviour, and make it so that if a NULL value is passed, that it causes Oracle to assign the explicit DEFAULT value that is specified in the function header?
I have considered the option of doing a manual check...
IF(varNumber IS NULL) THEN
varNumber := 0;
END IF;
However, there are hundreds of functions where this may be an issue, never mind the large number of parameters per function, and so I'd prefer it if I could find a more general solution to the problem.
Cheers for any insight you can give.
Use NVL to define the value.
NVL( value_in, replace_with )
You can't assign values to an IN parameter, but you could make them IN/OUT and then set them. That raises a big potential for misuse and confusion, though.
So I think you'd do better with a local variable. But you can do it in the declaration. That is,
create or replace
FUNCTION testFunction
(
varNumber IN NUMBER DEFAULT 0
)
RETURN NUMBER
AS
vFix number := nvl(varNumber,0);
BEGIN
dbms_output.put_line(vFix);
RETURN vFix;
END;
Your manual check is the only way to safely do what you want.
You can write that in one line like this though:
varNumber = NVL(varNumber,0);
Good luck!