[R] Conditionally Removing data from a vector

[Philipp Pagel]

> DEVS should equal 6 values the last being 620, like the data frame:
>            CANDS DEVS
> > [1,]   100  120
> > [2,]   101  220
> > [3,]   102  320
> > [4,]   103  420
> > [5,]   104  520
> > [6,]   105  620
> 
> And yes, my first question is do i need a "if" statement at all as the which
> command seems to do the same thing.

You don't - and you don't need which() either. R is pretty good
at indexing things in very conveniant ways. I'll assume we have
the data you gave as an example in a data.frame - I'll call 'df':

# create example data
df <- data.frame(cands=100:105, devs=c(120, 220, 320, 420, 520, 620))
threshold <- 400

# get all rows with devs above threshold
df[df$devs>threshold, ]

# alternative way giving the same result
subset(df, devs>threshold)


The above methods will work if devs and cands are separate
vectors, too:

# get two vectors of equal length
cands <- df$cands
devs <- df$devs

cands[devs>threshold]
# alternative
subset(cands, devs>threshold)


For details and more examples have a look at the "Introduction to
R" - especially section 2.7 "Index vectors; selecting and
modifying subsets of a data set".

cu
	Philipp

-- 
Dr. Philipp Pagel
Lehrstuhl für Genomorientierte Bioinformatik
Technische Universität München
Wissenschaftszentrum Weihenstephan
85350 Freising, Germany
http://mips.gsf.de/staff/pagel