[R] How to visualise what code is processed within a for loop

[Rui Barradas]

Hello,

instead of ifelse, the following is exactly the same and much more 
efficient.

d0[[nm]] <- as.integer(regexpr(d1[i,1], d0$X0) > 0)


Hope this helps,

Rui Barradas

On 4/28/2018 8:45 PM, Luca Meyer wrote:
> Thanks Don,
> 
>      for (i in 1:10){
>        nm <- paste0("V", i)
>        d0[[nm]] <- ifelse( regexpr(d1[i,1], d0$X0) > 0, 1, 0)
>      }
> 
> is exaclty what I needed.
> 
> Best regards,
> 
> Luca
> 
> 
> 2018-04-25 23:03 GMT+02:00 MacQueen, Don <macqueen1 using llnl.gov>:
> 
>> Your code doesn't make sense to me in a couple of ways.
>>
>> Inside the loop, the first line assigns a value to an object named "t".
>> Then, the second line does the same thing, assigns a value to an object
>> named "t".
>>
>> The value of the object named "t" after the second line will be the output
>> of the ifelse() expression, whatever that is. This has the effect of making
>> the first line irrelevant. Whatever value t has after the first line is
>> replaced by whatever it gets from the second line.
>>
>> It looks like the first line inside the loop is constructing the name of a
>> data frame column, and storing that name as a character string. However,
>> the second line doesn't use that name at all. If your goal is to update the
>> contents of a column, you need to assign something to that column in the
>> next line. Instead you assign it to the object named "t".
>>
>> What you're looking for will be more along the lines of this:
>>
>>      for (i in 1:10){
>>        nm <- paste0("V", i)
>>        d0[[nm]] <- ifelse( regexpr(d1[i,1], d0$X0) > 0, 1, 0)
>>      }
>>
>> This may not a complete solution, since I have no idea what the contents
>> or structure of d1 are, or what the regexpr() is expected to return.
>>
>> And notice the use of double brackets, [[ and ]]. This is one way to
>> reference a column of a  data frame when you have the column's name stored
>> in a variable. Another way is d0[ , nm]
>>
>>
>> A couple of additional comments:
>>
>>   "t" is a poor choice of object name, because it is one of R's built-in
>> functions (immediately after starting a fresh session of R, with nothing
>> left over from any previous session, type help("r") and see what you get).
>>
>>   ifelse() is intended for use on vectors, not scalars, and it looks like
>> maybe you're using it on a scalar (can't be sure about this, though)
>>
>> For example, ifelse() is designed for this kind of usage:
>>> ifelse( c(TRUE, FALSE, TRUE) , 1:3, 11:13)
>> [1]  1 12  3
>>
>> Although it works ok for these
>>> ifelse(TRUE, 3, 4)
>> [1] 3
>>> ifelse(FALSE, 3, 4)
>> [1] 4
>> They are not really what it is intended for.
>>
>> --
>> Don MacQueen
>> Lawrence Livermore National Laboratory
>> 7000 East Ave., L-627
>> Livermore, CA 94550
>> 925-423-1062
>> Lab cell 925-724-7509
>>
>>
>> On 4/24/18, 12:30 AM, "R-help on behalf of Luca Meyer" <
>> r-help-bounces using r-project.org on behalf of lucam1968 using gmail.com> wrote:
>>
>>      Hi,
>>
>>      I am trying to debug the following code:
>>
>>      for (i in 1:10){
>>        t <- paste("d0$V",i,sep="")
>>        t <- ifelse(regexpr(d1[i,1],d0$X0)>0,1,0)
>>      }
>>
>>      and I would like to see what code is actually processing R, how can I
>> do
>>      that?
>>
>>      More to the point, I am trying to update my variables d0$V1 to d0$V10
>>      according to the presence or absence of some text (contained in the
>> file
>>      d1) within the d0$X0 variable.
>>
>>      The code seem to run ok, if I add print(table(t)) within the loop I
>> can see
>>      that the ifelse procedure is working and to some cases within the
>> d0$V1 to
>>      d0$V10 variable range a 1 is assigned. But when checking my d0$V1 to
>> d0$V10
>>      after the for loop they are all still equal to zero...
>>
>>      Thanks,
>>
>>      Luca
>>
>>          [[alternative HTML version deleted]]
>>
>>      ______________________________________________
>>      R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
>>      https://stat.ethz.ch/mailman/listinfo/r-help
>>      PLEASE do read the posting guide http://www.R-project.org/
>> posting-guide.html
>>      and provide commented, minimal, self-contained, reproducible code.
>>
>>
>>
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>