for i in (0..5)
if(i==0)
i=4
end
puts i
end
In the above program I excepted the output as - 4 5
But instead it is - 4 1 2 3 4 5
So I conclude that loop variable isnt changing. How can change it? Can anyone tell me?
Actually, In my program I need to save the current state of loop and retrive later so that on the next start program resumes from the same point where it was left.
The only way you'll be able to modify the loop variable is to use a while loop:
x = (2..7).to_a
i = 0
while (i < x.length)
i = 4 if i == 0
puts x[i]
i = i + 1
end
Output:
6
7
In a for loop, as you've discovered, you can modify the loop variable and that value will hold for that iteration of the loop. On the next iteration, it will retrieve the next element from the range you specified so your modified value will essentially be overwritten.
There is no way to do that without a hack. The next best thing would be to use next.
x = (0..5).to_a
for i in (0..5)
if(i < 4)
next
end
puts x[i]
end
produces:
4
5
I am not sure how your code relates to the problem you are later mentioning. It looks to me that all you need to do is:
start_pos = load_start_pos || 0 # if not available for load, assume zero
(start_pos..end_pos).each do |i|
if need_to_exit?
save_start_pos i # save for later
break # exit the loop
end
end
Related
We are performing task as Accept a number as the seed value for math.randomseed(), and generate a random integer (interval [1,6]) using math.random() during each iteration of a loop, and continue the loop till the number is 6.
For which we had written code as
i = io.read()
local count = 0
math.randomseed(i)
for x = 1, 4 do
value = math.random(1, 6)
print(value)
count = count + 1
end
print(count)
We failed to pass test because
Input (stdin)
Run as Custom Input
0
Your Output (stdout)
3
5
5
6
2
Expected Output
3
5
5
6
4
Please help us
OP code seems to be having loop problems. I encourage the OP to read the Lua documentation about Control Structures, where Lua's while, repeat until, and goto are described, as well as the following manual section about Lua's For Statement. It is difficult to write any program in any language without understanding the fundamental control structures of the language.
OP problem can be solved in a variety of ways.
Using for
-- for version
i = io.read()
math.randomseed(i)
local count
for i = 1, math.huge do
local value = math.random(1, 6)
print(value)
count = i
if value == 6 then break end
end
print(count)
Here math.huge is the largest representable number in Lua, typically the special value inf, making this effectively an infinite loop. The variable i keeps track of how many random numbers have been generated, but since i will not be visible outside of the loop, the count variable is needed to copy the value of i so that it can be printed at the end.
Using while
-- while version
i = io.read()
math.randomseed(i)
local value = math.random(1, 6)
local count = 1
while value < 6 do
print(value)
count = count + 1
value = math.random(1, 6)
end
print(value)
print(count)
Here the looping construct begins with a test, so a test value must be created before the loop begins. This means that the count must be initialized to 1 before the loop begins, and it also means that the call to math.random will be duplicated. Not pretty.
Using repeat until
-- repeat until version
i = io.read()
math.randomseed(i)
local count = 0
repeat
local value = math.random(1, 6)
print(value)
count = count + 1
until value == 6
print(count)
Here the test comes at the end of the loop construct. This allows the code to call math.random only once.
Using goto
-- goto version
i = io.read()
math.randomseed(i)
local count = 0
::loop::
local value = math.random(1, 6)
print(value)
count = count + 1
if value < 6 then goto loop end
print(count)
You probably should not use goto to solve this problem, but you can. You have to be careful with goto in Lua; you can't jump into a block, out of a function, or into the scope of a local variable.
As you can see, there are some subtleties to these looping constructs, and using them requires some familiarity with the details.
All four versions produce identical outputs for the same inputs:
$ lua loops.lua
42
2
5
3
2
2
4
6
7
This question already has answers here:
Lua for loop reduce i? Weird behavior [duplicate]
(3 answers)
Closed 7 years ago.
im trying this in lua:
for i = 1, 10,1 do
print(i)
i = i+2
end
I would expect the following output:
1,4,7,10
However, it seems like i is getting not affected, so it gives me:
1,2,3,4,5,6,7,8,9,10
Can someone tell my a bit about the background concept and what is the right way to modify the counter variable?
As Colonel Thirty Two said, there is no way to modify a loop variable in Lua. Or rather more to the point, the loop counter in Lua is hidden from you. The variable i in your case is merely a copy of the counter's current value. So changing it does nothing; it will be overwritten by the actual hidden counter every time the loop cycles.
When you write a for loop in Lua, it always means exactly what it says. This is good, since it makes it abundantly clear when you're doing looping over a fixed sequence (whether a count or a set of data) and when you're doing something more complicated.
for is for fixed loops; if you want dynamic looping, you must use a while loop. That way, the reader of the code is aware that looping is not fixed; that it's under your control.
When using a Numeric for loop, you can change the increment by the third value, in your example you set it to 1.
To see what I mean:
for i = 1,10,3 do
print(i)
end
However this isn't always a practical solution, because often times you'll only want to modify the loop variable under specific conditions. When you wish to do this, you can use a while loop (or if you want your code to run at least once, a repeat loop):
local i = 1
while i < 10 do
print(i)
i = i + 1
end
Using a while loop you have full control over the condition, and any variables (be they global or upvalues).
All answers / comments so far only suggested while loops; here's two more ways of working around this problem:
If you always have the same step size, which just isn't 1, you can explicitly give the step size as in for i =start,end,stepdo … end, e.g. for i = 1, 10, 3 do … or for i = 10, 1, -1 do …. If you need varying step sizes, that won't work.
A "problem" with while-loops is that you always have to manually increment your counter and forgetting this in a sub-branch easily leads to infinite loops. I've seen the following pattern a few times:
local diff = 0
for i = 1, n do
i = i+diff
if i > n then break end
-- code here
-- and to change i for the next round, do something like
if some_condition then
diff = diff + 1 -- skip 1 forward
end
end
This way, you cannot forget incrementing i, and you still have the adjusted i available in your code. The deltas are also kept in a separate variable, so scanning this for bugs is relatively easy. (i autoincrements so must work, any assignment to i below the loop body's first line is an error, check whether you are/n't assigning diff, check branches, …)
I'm trying to find something in a loop in Lua, and when I'm done I need to use the location I found.
for j = 1,100 do
<do some stuff>
if <some test> then
break
end
end
if j >= 100 then
return
end
Unfortunately, I get an error which suggests that after the for loop exits, the value of j is nil. How do I use the value that j ended at? Obviously I could create an extra variable and assign it right before I break, but that just seems wrong, and I've never seen another language set the loop variable to nil when the loop ends, so I'm wondering if there isn't a better way to accomplish this.
The loop variable is only visible inside the for loop block. You can get around this by creating another variable as suggested in PIL 4.3.4 Numeric For.
local index
for j=1,100 do
if j == 10 then
index = j
end
end
Alternatively, if you are a doing a common operation then using a function with an early return may be best.
function find(tbl, val)
for i, v in ipairs(tbl) do
if v == val then
return i
end
end
end
I want to have a if condition within a loop. That is As long as id < 10,
check if Modc_initial is equal to MODC, if true then set d = 12
This is the code I tried bit not working, can anyone please help.
LOOP if (id LT 10)
IF(Modc_initial EQ MODC))
COMPUTE d = 12.
END LOOP.
EXECUTE.
You can either use a one line conditional of the form IF (condition) d = 12. or a multiple line DO IF. Below I provide an example of DO IF adapted to your syntax.
data list free / id MODC Modc_initial.
begin data
1 3 3
2 3 5
12 1 1
end data.
LOOP if (id LT 10).
DO IF (Modc_initial EQ MODC).
COMPUTE d = 12.
END IF.
END LOOP IF (d = 12).
EXECUTE.
Note you had a period missing in your original syntax on the initial LOOP. I also added an end loop condition, otherwise the code as written would just go until the maximum set number of loops per your system.
I am pretty new at SPSS macro's, but I think I need one.
I have 400 variables, I want to do this loop 400 times. My variables are ordered consecutively. So first I want to do this loop for variables 1 to 4, then for variables 5 to 8, then for variables 9 to 12 and so on.
vector TEQ5DBv=T0EQ5DNL to T4EQ5DNL.
loop #index = 1 to 4.
+ IF( MISSING(TEQ5DBv(#index+1))) TEQ5DBv(#index+1) = TEQ5DBv(#index) .
end loop.
EXECUTE.
Below is an example of what it appears to me you are trying to do. Note I replaced your use of the looping and index with a do repeat command. To me it is just more clear what you are doing by making two lists in the do repeat command as opposed to calling lead indexes in your loop.
*making data.
DATA LIST FIXED /X1 to X4 1-4.
BEGIN DATA
1111
0101
1 0
END DATA.
*I make new variables, so you dont overwrite your original variables.
vector X_rec (4,F1.0).
do repeat X_rec = X_rec1 to X_rec4 / X = X1 to X4.
compute X_rec = X.
end repeat.
execute.
do repeat X_later = X_rec2 to X_rec4 / X_early = X1 to X3.
if missing(X_later) = 1 X_later = X_early.
end repeat.
execute.
A few notes on this. Previously your code was overwriting your initial variables, in this code I create a set a new variables named "X_rec1 ... X_rec4", and then set those values to the same as the original set of variables (X1 to X4). The second do repeat command fills in the recoded variables if a missing value occurs with the previous variable. One big difference between this and your prior code, in your prior code if you ran it repeatedly it would continue to fill in the missing data, whereas my code would not. If you want to continue to fill in the missing data, you would just have to replace in the code above X_early = X1 to X3 with X_early = X_rec1 to X_rec3 and then just run the code at least 3 times (of course if you have a case with all missing data for the four variables, it will all still be missing.) Below is a macro to simplify calling this repeated code.
SET MPRINT ON.
DEFINE !missing_update (list = !TOKENS(1)).
!LET !list_rec = !CONCAT(!list,"_rec")
!LET !list_rec1 = !CONCAT(!list_rec,"1")
!LET !list_rec2 = !CONCAT(!list_rec,"2")
!LET !list_rec4 = !CONCAT(!list_rec,"4")
!LET !list_1 = !CONCAT(!list,"1")
!LET !list_3 = !CONCAT(!list,"3")
!LET !list_4 = !CONCAT(!list,"4")
vector !list_rec (4,F1.0).
do repeat UpdatedVar = !list_rec1 to !list_rec4 / OldVar = !list_1 to !list_4.
compute UpdatedVar = OldVar.
end repeat.
execute.
do repeat UpdatedVar = !list_rec2 to !list_rec4 / OldVar = !list_1 to !list_3.
if missing(UpdatedVar) = 1 UpdatedVar = OldVar.
end repeat.
execute.
!ENDDEFINE.
*dropping recoded variables I made before.
match files file = *
/drop X_rec1 to X_rec4.
execute.
!missing_update list = X.
I suspect there is a way to loop through all of the variables in the dataset without having to call the macro repeatedly for each set, but I'm not sure how to do it (it may not be possible within DEFINE, and you may have to resort to writing up a python program). Worst case you just have to write the above macro defined function 400 times!
Your Loop-Syntax is incorrect because when #index reaches "4" your code says that you want to do an operation on TEQ5DBv(5). So you definetly will get an error.
I don't know what exactly you want to do, but a nested loop might help you to achieve your goal.
Here is an example:
* Creating some Data.
DATA LIST FIXED /v1 to v12 1-12.
BEGIN DATA
1234 9012
2 4 6 8 1 2
1 3 5 7 9 1
12 56 90
456 012
END DATA.
* Vectorset of variables
VECTOR vv = v1 TO v12.
LOOP #i = 1 TO 12 BY 4.
LOOP #j = 0 TO 2. /* inner Loop runs only up to "2" so you wont exceed your inner block.
IF(MISSING(vv(#i+#j+1))) vv(#i+#j+1) = vv(#i+#j).
END LOOP.
END LOOP.
EXECUTE.