Re: [R] recoding data with loops

From: Donald Braman <donald.braman_at_gmail.com>
Date: Mon, 19 May 2008 16:12:53 -0400

Many thanks --

You are right; I had rnorm() and sample() mixed up in my code. I'll work on generating a normal ordinal sample next.

Cheers, Don

On Mon, May 19, 2008 at 4:07 PM, Erik Iverson <iverson_at_biostat.wisc.edu> wrote:

> Hello -
>
> Donald Braman wrote:
>

>> # I'm new to R and am trying to get the hang of how it handles
>> # dataframes & loops. If anyone can help me with some simple tasks,
>> # I'd be much obliged.
>>
>> # First, i'd like to generate some random data in a dataframe
>> # to efficiently illustrate what I'm up to.
>> # let's say I have six variables as listed below (I really
>> # have hundreds, but a few will illustrate the point).
>> # I want to generate my dataframe (mdf)
>> # with the 6 variables X 100 values with rnorm(7).
>> # How do I do this? I tried many variations on the following:

>>
>> var_list <- c("HEQUAL", "EWEALTH", "ERADEQ", "HREVDIS1", "EDISCRIM",
>> "HREVDIS2")
>> for(i in 1:length(var_list)) {var_list[1] <- rnorm(100)}
>> mdf <- data.frame(cbind(varlist[1:length(var_list)])
>> mdf
>>
>> There are many ways to do this. Do you mean that you want 6 columns, 100
> observations in each column, each a sample from a normal distribution with
> mean = 7 and sd = 1? You can do this without looping in one of several
> ways. If you are coming from a SAS environment (my guess since you talk of
> looping over data.frames), you may be used to looping through a data object.
> In R, you can usually avoid this since many functions are vectorized, or
> take a 'whole object' approach.
>
> var_list <- c("HEQUAL", "EWEALTH", "ERADEQ", "HREVDIS1", "EDISCRIM",
> "HREVDIS2")
>
> mdf <- data.frame(replicate(6, rnorm(100, 7))) ## generate random data
> names(mdf) ## default names
> names(mdf) <- var_list ## use our names
>
>
>> # Then, I'd like to recode the variables that begin with the letter "H".
>> # I've tried many variations of the following, but to no avail:

>>
>> reverse_list <- c("HEQUAL", "HREVDIS1", "HREVDIS2")
>> reversed_list <- c("RHEQUAL", "RHREVDIS1", "RHREVDIS2")
>> for(i in 1:length(reverse_list))
>> {mdf[ ,e_reversed_list][[i]] <- recode(mdf[ ,e_reverse_list][[i]],
>> '5:99=NA; 1=4; 2=3; 3=2; 4=1; ', as.factor.result=FALSE)
>>
>>
> I'm not quite sure what you are after here. What do you mean by recode?
> What package is your 'recode' function located in?
>
> It appears that you may be under the impression that the data.frame
> contains integers, but certainly it will not since it was generated with
> rnorm? sample can generate a samples of the type you may be after, for
> example,
>
> > sample(7, 100, replace = TRUE)
>
> Best,
> Erik Iverson
>

-- 
Donald Braman
http://www.law.gwu.edu/Faculty/profile.aspx?id=10123
http://research.yale.edu/culturalcognition
http://ssrn.com/author=286206

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