do-while loop in R

Question

I was wondering about how to write do-while-style loop   I found this post      you can use repeat   and check conditions whereever using if      and   exit the loop with the  break  control word    I am not sure what it exactly means  Can someone please elaborate if you understand it and or if you have a different solution

User · Accepted Answer

Pretty self explanatory   repeat    statements      if condition       break         Or something like that I would think  To get the effect of the do while loop  simply check for your condition at the end of the group of statements

User · Answer

See  Control or  the R Language Definition    gt  y 0  gt  while y  lt 5   print  y lt -y 1     1  1  1  2  1  3  1  4  1  5   So do while does not exist as a separate construct in R  but you can fake it with   repeat    expressions   if    end cond expr    break      If you want to see the help page you cannot type  while or  repeat at the console but rather need to use   repeat  or   while   All the  control-constructs  including if are on the same page and all need character quoting after the     so the interpreter doesn t see them as incomplete code and give you a continuation

User · Answer

Noticing that user 42- s perfect approach      do while     repeat until not    The code equivalence   do while  condition    in other language   statements   endo  repeat    in R     statements     if   condition   break     Negation is crucial here        did not receive enough attention from the others  I ll emphasize and bring forward his approach via a concrete example  If one does not negate the condition in do-while  via   or by taking negation   then distorted situations  1  value persistence 2  infinite loop  exist depending on the course of the code   In Gauss   proc 0  printvalues y   DO WHILE y  lt  5      y 1   y y 1  ENDO  ENDP  printvalues 0     run selected code via F4 to get the following          1 0000000         2 0000000         3 0000000         4 0000000         5 0000000    In R   printvalues  lt - function y    repeat    y y 1  print y  if     y  lt  5     break      Negation is crucial here      printvalues 0     1  1    1  2    1  3    1  4    1  5   I still insist that without the negation of the condition in do-while  Salcedo s answer is wrong  One can check this via removing negation symbol in the above code

User · Answer

Building on the other answers  I wanted to share an example of using the while loop construct to achieve a do-while behaviour  By using a simple boolean variable in the while condition  initialized to TRUE   and then checking our actual condition later in the if statement  One could also use a break keyword instead of the continue  lt - FALSE inside the if statement  probably more efficient       df  lt - data frame X c    R c        x  lt - x0   continue  lt - TRUE    while continue          xi  lt -  11   x     16     df  lt - rbind df  data frame X x  R xi       x  lt - xi      if xi    x0              continue  lt - FALSE

[r] do-while loop in R

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