val x =10;
fun power (x:int, y:int) =
if y=1
then x
else
x * power (x,y-1)
val z = power 2,3
It gives me an error Replacing COMMA with EQUALOP . I dont understand whats the error in the code ??
You need parentheses around the argument to power in the declaration of z:
val z = power (2,3);
Related
I am new to Nim, and wrote this simple code for fun:
var x: int = 3
var y: int = 4
if true:
y = 7
else:
x = 7
proc hello(xx: int, yy: int, ): int =
return xx + yy
hello(x, y)
The code seems fine (I checked with the Nim manuals), but it gives this weird error:
c:\Users\Xilpex\Desktop\Nim_tests\testrig.nim(12, 6) Error: expression 'hello(x, y)' is of type 'int' and has to be discarded
Why am I getting this error? Is there something I can do to fix it?
You are getting an error because procs declared to return values are meant to use that value somewhere, so the compiler reminds you that you are forgetting the result of the call. If some times you want the result, and others you want to ignore it, instead of creating a temporal variable you can use the discard statement or declare the proc as {.discardable.}.
I just found out why I was getting that error... It was because the procedure returned a value, and I wasn't storing that value anywhere. Here is the working code:
var x: int = 3
var y: int = 4
if true:
y = 7
else:
x = 7
proc hello(xx: int, yy: int, ): int =
return xx + yy
var output = hello(x, y)
I want to create a new variable in Stata, that is a function of 3 different variables, X, Y and Z, like:
gen new_var = (((X)*3) + ((Y)*2) + ((Z)*4))/7
All observations have missing values for one or two of the variables.
When I run the aforementioned command, all it generates are missing values, because no observation has values for all 3 of the variables. I would like Stata to complete the function ignoring the missing variables.
I tried the following commands without success:
gen new_var= (cond(missing(X*3),., X) + cond(missing(Y*2),., Y))/7
gen new_var= (!missing(X*3+Y*2+Z*4)/7)
gen new_var= (max(X , Y, Z)/7) if missing(X , Y, Z)
The egen command does not allow complicated functions; otherwise rowtotal() could work.
EDIT:
To clarify, "ignoring missing variables" means that even if any one of the component variables is not missing, then apply the function to only that variable and produce a value for the new variable. The new variable should have missing values only when all three component variables are missing.
I am going to guess that "ignoring missing values" means "treating them as zeros". If you have some other idea, you should make it explicit.
That could be
gen new_var = (cond(missing(X), 0, 3 * X) ///
+ cond(missing(Y), 0, 2 * Y) ///
+ cond(missing(Z), 0, 4 * Z)) / 7
Let's look at your solutions and explain why they are all wrong either in general or usually.
(cond(missing(X*3),., X) + cond(missing(Y*2),., Y))/7
It is sufficient is note that if it's true that X is missing, then cond() yields missing, as then X * 3 is missing too. The same kind of remark applies to terms involving Y and Z. So you're replacing any missing values by missing values, which is no gain.
!missing(X*3+Y*2+Z*4)/7
Given the information that at least one of X Y Z is always missing, then this always evaluates to 0/7 or 0. Even if X Y Z were all non-missing, then it would evaluate to 1/7. That is a long way from the sum you want. missing() always yields 1 or 0, and its negation thus 0 or 1.
(max(X, Y, Z)/7) if missing(X , Y, Z)
The maximum of X, Y, Z will be the right answer if and only if one of the values is not missing and the other two are missing. max() ignores missings to the extent possible (even though in other contexts missings are treated as if arbitrarily large positive numbers).
If you just want to "ignore missing values" without "treating them as zeros", the following will work:
clear
set obs 10
generate X = rnormal(5, 2)
generate Y = rnormal(10, 5)
generate Z = rnormal(1, 10)
replace X = . in 2
replace Y = . in 5
replace Z = . in 9
generate new_var = (((X)*3) + ((Y)*2) + ((Z)*4)) / 7 if X != . | Y != . | Z != .
list
+---------------------------------------------+
| X Y Z new_var |
|---------------------------------------------|
1. | 3.651024 3.48609 -24.1695 -11.25039 |
2. | . 14.14995 8.232919 . |
3. | 3.689442 9.812483 1.154064 5.044221 |
4. | 2.500493 13.02909 5.25539 7.797317 |
5. | 4.19431 . 6.584174 . |
6. | 7.221717 13.92533 5.045283 9.956708 |
7. | 5.746871 14.26329 3.828253 8.725744 |
8. | 1.396223 16.2358 19.01479 16.10277 |
9. | 4.633088 13.95751 . . |
10. | 2.521546 4.490258 -3.396854 .422534 |
+---------------------------------------------+
Alternatively, you could also use the inlist() function:
generate new_var = (((X)*3) + ((Y)*2) + ((Z)*4)) / 7 if !inlist(., X, Y, Z)
I have written the program below and keep getting the error message that my variables are not defined.
Can somebody plese see where the error is and how I should adapt the code? Really nothing seems to work.
program define myreg, rclass
drop all
set obs 200
gen x= 2*uniform()
gen z = rnormal(0,1)
gen e = (invnorm(uniform()))^2
e=e-r(mean)
replace e=e-r(mean)
more
gen y = 1 + 1*x +1*z + 1*e
reg y x z
e=e-r(mean)
replace e=e-r(mean)
more
gen y = 1 + 1*x +1*z + 1*e
reg y x z
more
return scalar b0 =_[_cons]
return scalar b1=_[x]
return scalar b2 =_[z]
more
end
simulate b_0 = r(b0) b_1 = r(b1) b_2 = r(b2), rep(1000): myreg
*A possible solution with eclass
capture program drop myreg
program define myreg, eclass
* create an empty data by dropping all variables
drop _all
set obs 200
gen x= 2*uniform()
gen z = rnormal(0,1)
gen e = (invnorm(uniform()))^2
qui sum e /*to get r(mean) you need to run sum first*/
replace e=e-r(mean)
gen y = 1 + 1*x +1*z + 1*e
reg y x z
end
*gather the coefficients (_b) and standard errors (_se) from the *regression each time
simulate _b _se, reps(1000) seed (123): myreg
* show the final result
mat list r(table)
* A possible solution with rclass
* To understand the difference between rclass and eclass, see the Stata manual(http://www.stata.com/manuals13/rstoredresults.pdf)
capture program drop myreg
program define myreg, rclass
drop _all
set obs 200
gen x= 2*uniform()
gen z = rnormal(0,1)
gen e = (invnorm(uniform()))^2
qui sum e
replace e=e-r(mean)
gen y = 1 + 1*x +1*z + 1*e
reg y x z
mat output=e(b)
return scalar b0=output[1,3]
return scalar b1=output[1,1]
return scalar b2=output[1,2]
end
simulate b_0=r(b0) b_1=r(b1) b_2=r(b2), rep(1000) seed (123): myreg
return list
*P.S. You should read all the comments as suggested by #Nick to fully understand what I did here. .
Hi everyone I'm newbie in prolog and I have such a list: (actually It is output of my predicate not a list )
P = [1/1, 1/3] ;
P = [1/1, 2/3] ;
P = [1/3, 1/1] ;
P = [1/3, 2/1] ;
P = [2/1, 1/3] ;
P = [2/1, 2/3] ;
P = [2/3, 1/1] ;
P = [2/3, 2/1] ;
and I need to remove dublicete terms.For example [1/1,2/3] and [2/3,1/1]is same and I should remove one of them , which one is not important ,How could I do that in prolog ?? Thanks in advance
NOTE I LEARNT THAT findALL should be good way for this but still dont know the answer please help me .
Unless you actually show us your code, it's never going to be possible to give you precise answers.
I assume you have a predicate f/1 such that:
?- f(P).
produces the interactive result you show above. A simple solution is to change your query:
?- f([X,Y]), X < Y.
This will produce the following result:
X = 1/3, Y = 1/1 ;
X = 1/3, Y = 2/1 ;
X = 2/3, Y = 1/1 ;
X = 2/3, Y = 2/1 ;
findall/3 isn't sufficient to solve this particular situation, because you've defined uniqueness in a way that ignores the position in the list. In Prolog (and everything else) [X,Y] and [Y,X] are not equal, so you'd have to find a trick to get this to give you "unique" results.
I have this SML code. I don't know why I cannot compile this :
fun score =
let
val sum = 3; (* error at this line : SYNTAX ERROR : inserting LPAREN *)
if sum div 2 > 0
then sum = 0
else sum = 1
(*some other code*)
in
sum (* I want to return sum after some steps of calculation *)
end
There are more issues with your code, than jacobm points out.
You are also missing a function argument. Functions in SML always takes one argument. For example
fun score () =
let val sum = 3
val sum = if sum div 2 > 0
then sum = 0
else sum = 1
in
sum
end
However this still doesn't make much sense. since the expressions sum = 0 and sum = 1 evaluates to a Boolean.
A let-expression is used to make some local declarations which are only visible inside the in ... end part. Thus the calculations you wan't to do with sum, should probably be done inside the in ... end part, unless you wan't to express it as a means of a function.
One such example is
fun score () =
let val sum = 3
in
if sum div 2 > 0
then ...
else ...
end
If we look at the syntax of a let-expression, it probably makes more sense
let
<declaration>
in
<expr> ; ... ; <expr>
end
Since if-then-else is an expression, it can't be in the "declarations part" by itself.
That syntax just isn't legal -- in between let and in all you're allowed to have is a series of val name = expr fragments. You can do this, though:
fun score =
let val sum = 3
val sum = if sum div 2 > 0
then sum = 0
else sum = 1
in
sum
end
I would consider it a bit of a weird style to use sum for both variable names, but it's legal.