R help - Feb 2008 - Looping through a list of objects & do something...

Hey Folks,

Could somebody show me how to loop through a list of dataframes?  I want to
be able to generically access their elements and do something with them.

For instance, instead of this:

df1<- data.frame(x=(1:5),y=(1:5));
df2<- data.frame(x=(1:5),y=(1:5));
df3<- data.frame(x=(1:5),y=(1:5));
plot(df1$x,df1$y);
plot(df2$x,df2$y);
plot(df3$x,df3$y);

I would like to do something like:
(pseudocode)
dfarray[1] = df1
dfarray[2] = df2
dfarray[3] = df3
for (each i in dfarray) {
  plot(i$x, i$y);
}

Can this be done in R?

Thanks.
Tripp


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On 2/19/2008 1:51 PM, TLowe wrote:
> Hey Folks,
> 
> Could somebody show me how to loop through a list of dataframes?  I want to
> be able to generically access their elements and do something with them.
> 
> For instance, instead of this:
> 
> df1<- data.frame(x=(1:5),y=(1:5));
> df2<- data.frame(x=(1:5),y=(1:5));
> df3<- data.frame(x=(1:5),y=(1:5));
> plot(df1$x,df1$y);
> plot(df2$x,df2$y);
> plot(df3$x,df3$y);
> 
> I would like to do something like:
> (pseudocode)
> dfarray[1] = df1
> dfarray[2] = df2
> dfarray[3] = df3
> for (each i in dfarray) {
>   plot(i$x, i$y);
> }
> 
> Can this be done in R?
Yes, easily:

dfarray <- list(df1, df2, df3)
lapply(dfarray, function(i) plot(i$x, i$y))

Duncan Murdoch

On Tuesday 19 February 2008 (19:51:15), TLowe wrote:
> Hey Folks,
>
> Could somebody show me how to loop through a list of dataframes?  I want to
> be able to generically access their elements and do something with them.
>
> For instance, instead of this:
>
> df1<- data.frame(x=(1:5),y=(1:5));
> df2<- data.frame(x=(1:5),y=(1:5));
> df3<- data.frame(x=(1:5),y=(1:5));
> plot(df1$x,df1$y);
> plot(df2$x,df2$y);
> plot(df3$x,df3$y);
>
> I would like to do something like:
> (pseudocode)
> dfarray[1] = df1
> dfarray[2] = df2
> dfarray[3] = df3
> for (each i in dfarray) {
>   plot(i$x, i$y);
> }
It's surprisingly simple:

for(df in list(df1,df2,df3)) plot(df$x,df$y)

Best,

Martin