understanding how R determines numbers and characters when creating a data frame

Hello R Users and Developers,

I have a basic question about how R works.  Over the past few years I have
struggled when I try to generate a new data frame that I believe should
contain numeric data in some columns and character data in others only to
find everything converted to character data. Is there a general method to
create data frames that contain the data in the desired format:  numbers as
numeric and character as a factor etc?  I often have this problem and in the
worst case I have to export the file and read it back it in.    I have
emulated a simple example of the problem.  It often happens while using
"for" loops.  Could someone explain how to avoid this problem by properly
creating data frames in for loops that can contain both numeric and
character data.

 

********Question for example 1.

Why does the cbind command convert the numeric data to character data?  Why
can't the character data be converted to numeric data using the fix command?
  

### Example 1  #############

data(iris)

obsnum<-NULL

results<-NULL

for(s in unique(as.character(iris$Species))){

temp1<-iris[iris$Species==s,]

obsnum<-length(unique(temp1$Sepal.Length))  # a number

  

out1<-cbind(species=as.character(paste(s)),obsnum)  # number converted to
character
  

results<-rbind(out1,results)

}

results

#fix(results)  # cannot convert obsnum to numeric using fix

####################################

 

******Question for example 2

Why does adding the data.frame command allow the character data to be
converted to numeric data using fix command?

### Example 2  #############

data(iris)

obsnum<-NULL

results<-NULL

for(s in unique(as.character(iris$Species))){

temp1<-iris[iris$Species==s,]

obsnum<-length(unique(temp1$Sepal.Length))

out1<-data.frame(cbind(species=as.character(paste(s)),obsnum)) # number
converted to character

results<-rbind(out1,results)

}

results

#fix(results)  # can now convert obsnum to numeric using fix

 

######

 

 

Thank you,

Alan Smith


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