[R] dependent nested for loops in R

[David Winsemius]

Sent from my iPhone

> On Feb 1, 2021, at 10:16 PM, David Winsemius <dwinsemius using comcast.net> wrote:
> 
> Or perhaps: 
> 
> W <- 1:2000
> W[z>4|z<2] <- 0

Another way:

W <- (1:2000)*(z>4|z<2)

As I said earlier you really should study logical class vectors and the operators that use them and how to apply them as indices. 
> Sent from my iPhone
> 
>>> On Feb 1, 2021, at 9:56 PM, David Winsemius <dwinsemius using comcast.net> wrote:
>>> 
>> Or perhaps you wanted:
>> 
>> W <- z
>> W[z>4|z<2] <- 0
>> 
>> Sent from my iPhone
>> 
>>>> On Feb 1, 2021, at 9:41 PM, David Winsemius <dwinsemius using comcast.net> wrote:
>>>> 
>>> Just drop the “+” if you want logical. 
>>> 
>>> Sent from my iPhone
>>> 
>>>>> On Feb 1, 2021, at 9:36 PM, Shaami <nzshaam using gmail.com> wrote:
>>>>> 
>>>> 
>>>> Hi Prof. David
>>>> 
>>>> Thank you. I will always follow your advice. The suggested code worked. It gives either 1 or 0 depending on the condition to be true. I want index of z for which the condition is true (instead of 1) else zero. Could you please suggest? 
>>>> 
>>>> Thank you
>>>> 
>>>> Shaami
>>>> 
>>>>> On Tue, Feb 2, 2021 at 10:16 AM David Winsemius <dwinsemius using comcast.net> wrote:
>>>>> Cc’ed the list as should always be your practice. 
>>>>> 
>>>>> Here’s one way (untested):
>>>>> 
>>>>> W <- +(z>4| z<2) # assume z is of length 20
>>>>> 
>>>>> — 
>>>>> David
>>>>> 
>>>>> Sent from my iPhone
>>>>> 
>>>>>>> On Feb 1, 2021, at 7:08 PM, Shaami <nzshaam using gmail.com> wrote:
>>>>>>> 
>>>>>> 
>>>>>> Hi Prof. David
>>>>>> 
>>>>>> In the following state
>>>>>> 
>>>>>> W = (1:2000)[z >4|z<2)
>>>>>> 
>>>>>> Could you please guide how  I can assign zero if condition is not satisfied?
>>>>>> 
>>>>>> Best Regards 
>>>>>> 
>>>>>> Shaami
>>>>>> 
>>>>>>> On Mon, 1 Feb 2021, 11:01 am David Winsemius, <dwinsemius using comcast.net> wrote:
>>>>>>> 
>>>>>>> On 1/31/21 1:26 PM, Berry, Charles wrote:
>>>>>>> >
>>>>>>> >> On Jan 30, 2021, at 9:32 PM, Shaami <nzshaam using gmail.com> wrote:
>>>>>>> >>
>>>>>>> >> Hi
>>>>>>> >> I have made the sample code again. Could you please guide how to use
>>>>>>> >> vectorization for variables whose next value depends on the previous one?
>>>>>>> >>
>>>>>>> 
>>>>>>> I agree with Charles that I suspect your results are not what you 
>>>>>>> expect. You should try using cat or print to output intermediate results 
>>>>>>> to the console. I would suggest you limit your examination to a more 
>>>>>>> manageable length, say the first 10 results while you are working out 
>>>>>>> your logic. After you have the logic debugged, you can move on to long 
>>>>>>> sequences.
>>>>>>> 
>>>>>>> 
>>>>>>> This is my suggestion for a more compact solution (at least for the 
>>>>>>> inner loop calculation):
>>>>>>> 
>>>>>>> set.seed(123)
>>>>>>> 
>>>>>>> x <- rnorm(2000)
>>>>>>> 
>>>>>>> z <- Reduce( function(x,y) { sum(y+5*x) }, x, accumulate=TRUE)
>>>>>>> 
>>>>>>> w<- numeric(2000)
>>>>>>> 
>>>>>>> w <-  (1:2000)[ z >4 | z < 1 ]  # In your version the w values get 
>>>>>>> overwritten and end up all being 2000
>>>>>>> 
>>>>>>> 
>>>>>>> I would also advise making a natural language statement of the problem 
>>>>>>> and goals. I'm thinking that you may be missing certain aspects of the 
>>>>>>> underying problem.
>>>>>>> 
>>>>>>> -- 
>>>>>>> 
>>>>>>> David.
>>>>>>> 
>>>>>>> >
>>>>>>> > Glad to help.
>>>>>>> >
>>>>>>> > First, it could help you to trace your code.  I suspect that the results are not at all what you want and tracing would help you see that.
>>>>>>> >
>>>>>>> > I suggest running this revision and printing out x, z, and w.
>>>>>>> >
>>>>>>> > #+begin_src R
>>>>>>> >    w = NULL
>>>>>>> >    for(j in 1:2)
>>>>>>> >    {
>>>>>>> >      z = NULL
>>>>>>> >      x = rnorm(10)
>>>>>>> >      z[1] = x[1]
>>>>>>> >      for(i in 2:10)
>>>>>>> >      {
>>>>>>> >        z[i] = x[i]+5*z[i-1]
>>>>>>> >        if(z[i]>4 | z[i]<1) {
>>>>>>> >       w[j]=i
>>>>>>> >        } else {
>>>>>>> >       w[j] = 0
>>>>>>> >        }
>>>>>>> >      }
>>>>>>> >    }
>>>>>>> > #+end_src
>>>>>>> >
>>>>>>> >
>>>>>>> > You should be able to see that the value of w can easily be obtained outside of the `i' loop.
>>>>>>> >

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