# Re: [R] help with simple function

From: T.D.Rudolph <prairie.picker_at_gmail.com>
Date: Tue, 27 May 2008 17:04:40 -0700 (PDT)

In fact x[4,2] should = log(x[5,1]/2]
whereas x[3,2] = log(x[5,1/3])

i.e. The denominator in the log function equals the number of rows between m==0 and m>0 (inclusive, hence the "+1")

Hope this helps!...

Charles C. Berry wrote:
>
> On Tue, 27 May 2008, T.D.Rudolph wrote:
>

```>>
>>
>> I have a matrix of frequency counts from 0-160.
>> x<-as.matrix(c(0,1,0,0,1,0,0,0,1,0,0,0,0,1))
>>
>> I would like to apply a function creating a new column (x[,2])containing
>> values equal to:
>> a) log(x[m,1]) if x[m,1] > 0; and
>> b) for all x[m,1]= 0, log(next x[m,1] > 0 / count of preceding zero
>> values
>> +1)
>>
>> for example, x[1,2] should equal log(x[2,1]/2) = log(1/2) = -0.6931472
>> whereas x[3,2] should equal log(x[5,1]/3) = log (1/3) = -1.098612
>>
```

>
> If you also intend that x[4,2] == x[3,2] in your example, then this seems
> what you want:
>
```>> rle.x <- rle(x[,1])
>> num <- ifelse(rle.x\$values == 0, c(tail(rle.x\$values,-1),NA),
>> rle.x\$values )
>> denom <- ifelse(rle.x\$values == 0 , rle.x\$lengths +1 , 1 )
>> rep(log(num/denom),rle.x\$lengths)
```

> [1] -0.6931472 0.0000000 -1.0986123 -1.0986123 0.0000000 -1.3862944
> -1.3862944 -1.3862944 0.0000000 -1.6094379
> [11] -1.6094379 -1.6094379 -1.6094379 0.0000000
```>>
```

>
> See
>
> ?rep
> ?rle
> ?tail
>
> HTH,
>
> Chuck
>
>
```>> I will be applying this to nrow(x)=~70,000 so I would prefer to not do it
>> by
>> hand!
>> Tyler
>>
>>
>>
>> --
>> View this message in context:
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>>
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>> and provide commented, minimal, self-contained, reproducible code.
>>

>
> Charles C. Berry                            (858) 534-2098

>                                              Dept of Family/Preventive
> Medicine
> E mailto:cberry_at_tajo.ucsd.edu	            UC San Diego
```
> http://famprevmed.ucsd.edu/faculty/cberry/ La Jolla, San Diego 92093-0901
>
> ______________________________________________
> R-help_at_r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
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> and provide commented, minimal, self-contained, reproducible code.
>
>
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