[R] Correct Syntax for a Loop
Uwe Ligges
ligges at statistik.uni-dortmund.de
Sun Nov 28 13:10:47 CET 2004
ebashi wrote:
> I'll appreciate if some one can help me with the
> following loop. This is the logic of the loop,
> if we have the following data;
>
>>x.df
>
> x.dif
> . .
> . .
> 102 0.00
> 103 0.42
> 104 0.08
> 105 0.00
> 106 0.00
> 107 0.00
> 108 -0.16
> 109 -0.34
> 110 0.00
> 111 -0.17
> 112 -0.33
> 113 0.00
> 114 0.00
> 115 0.00
> 116 0.33
> 117 0.17
> 118 0.00
> . .
> . .
> I'm trying to find i's where
> for (i in 2:length(x.dif))
> if (x.dif[i-1]<=0 and x.dif[i]>0 and x.dif[i+2]>0)
Solution to the question:
a) you cannot loop to length(x.dif), x.dif[i+2] does not exist for
i==length(x.dif).
b) Use && instead of "and" in this case
c) vector operations are much mor
Hint: If you lengthen the vectors appropriately, you can apply the
comparisons vectorized rather than in a loop...
Uwe Ligges
> it would return i+2 to me,
> How can I turn this to a right format as a loop.(I
> can't figure out the syntax)
>
> Cheers,
>
> Sean
>
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