[R] Help with creating some loops

[David Winsemius]

On Oct 30, 2009, at 11:24 AM, Vadlamani, Satish {FLNA} wrote:

> Hi:
> In general, how to I cast a character to the class that I am trying  
> to change.
>
> For example, if I have a data frame df1. df1 has a column x. suppose  
> I want to a substring of x (the first 3 chars). Then I want to do  
> something like
>
> df1$new = substring(of x)
>
> Example
> Data frame df1
> x
> abcd
> efgh
>
> Now df1$new should be
> ab
> ef

Following your written specification (rather than your example):

 > df1 <- data.frame(x=c("abcd", "efgh"))
 > df1
      x
1 abcd
2 efgh
 > df1$new <- substr(df1$x,start=1,stop=3)
 > df1
      x new
1 abcd abc
2 efgh efg


>
> Thanks.
> Satish
>
>
>
> _____________________________________________
> From:   Vadlamani, Satish {FLNA}
> Sent:   Friday, October 30, 2009 8:40 AM
> To:     R-help at r-project.org
> Subject:        Help with creating some loops
>
> Hi All:
>
> I have a data frame called all_corn. This has 31 columns. The first  
> column is a character key. The next 15 columns  
> (stat1,stat2,...,stat15) are the statistical forecast. The last 15  
> columns (sls1,sls2,...,sls5) are actual sales.
> I want to calculate textbook tracking signal and cuulative percent  
> error.
>
> 1) I am showing some of the calculations below. How can I make a  
> loop out of this instead of manually doing this 15 times?
> 2) Once All these calculations are done, how do I put all these  
> columns (err1,err2, etc.) into the same data frame?
>
> Thanks.
>
> attach(all_corn)
>
> cum_sls1 <- sls1
> err1 <- sls1-stat1
> cum_err1 <- sls1-stat1
> cum_abs_err1 <- abs(err1)
> mad1 <- abs(cum_err1)/1
> cum_pct_err1 <- (ifelse(cum_sls1 > 0, cum_err1/cum_sls1, 1))*100
> ts1 <- ifelse(mad1 > 0, cum_err1/mad1, 0)
>
> cum_sls2 <- cum_sls1 + sls2
> err2 <- sls2-stat2
> cum_err2 <- cum_err1 + sls2-stat2
> cum_abs_err2 <- cum_abs_err1 + abs(err2)
> mad2 <- cum_abs_err2/2
> cum_pct_err2 <- (ifelse(cum_sls2 > 0, cum_err2/cum_sls2, 1))*100
> ts2 <- ifelse(mad2 > 0, cum_err2/mad2, 0)
>
> ______________________________________________
> R-help at r-project.org mailing list
> 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.

David Winsemius, MD
Heritage Laboratories
West Hartford, CT