R help - Sep 2009 - Help with sub-setting data.frame

Friends

I have a data frame, df that I want to extract some rows from

Here is a sample of the data
> head(df)
     TDate Expiry Underlie Strike CSettle PSettle Futures   ExDate
TTE
1 20080102 200801   200803  0.840  0.0000       0  0.9207 20080104
0.005479452
2 20080102 200801   200803  0.850  0.0000       0  0.9207 20080104
0.005479452
    Rate      Disc
1 0.0457 0.9997496
2 0.0457 0.9997496

I want all rows where TTE is equal to 0.024657534
> head(summary(factor(df[,"TTE"])), n=1)
0.024657534
        602

Using...

head(df["TTE">=0.02])
I get
> head(df["TTE">=0.02])
     TDate Expiry Underlie Strike CSettle PSettle Futures   ExDate
TTE
1 20080102 200801   200803  0.840  0.0000       0  0.9207 20080104
0.005479452
2 20080102 200801   200803  0.850  0.0000       0  0.9207 20080104
0.005479452
    Rate      Disc
1 0.0457 0.9997496
2 0.0457 0.9997496

Which is obviously not working.  How can I make it work?

I can do
> tte.CSettle <- df[c("TTE", "CSettle")]
> tte.1 <- tte.CSettle[tte.CSettle<0.03,]
> tte.2 <- tte.1[tte.1>0.02,]
> head(tte.2)
           TTE CSettle
582 0.02465753  0.0000
583 0.02465753  0.0000
> tail(tte.2)
         TTE CSettle
NA.72617  NA      NA
NA.72618  NA      NA
>
So I have introduced a lot of NAs that were not there before.

I think I have done this before I just cannot remember how.  The
Extract.data.frame help page does not tell me how.

cheers
Worik
worik.stanton@gmail.com

	[[alternative HTML version deleted]]

On Wed, 2 Sep 2009 17:12:18 +1200 Worik R <worikr at gmail.com> wrote:

WR> I have a data frame, df that I want to extract some rows from

What you need is subset, see
?subset

Example:
df<-data.frame(TTE=(0:10)/100,SOME=rnorm(11))
df
# subset with all columns
subset(df,TTE<0.02)
# the same as:
df[df$TTE<0.02,]

When you put the whole data.frame into the braces it does not make much
sense...

hth
Stefan

Your subset problem has been solved already but i'd like to add a
comment on this:
> I want all rows where TTE is equal to 0.024657534
Comparing floating point numbers for equality with '==' is problematic
so a simple df[df$TTE == 0.024657534, ] can easily fail. have a look
at help("=="), especially the note on numerical values and the
exmaples.

cu
	Philipp

-- 
Dr. Philipp Pagel
Lehrstuhl f?r Genomorientierte Bioinformatik
Technische Universit?t M?nchen
Wissenschaftszentrum Weihenstephan
85350 Freising, Germany
http://webclu.bio.wzw.tum.de/~pagel/