[R] [PS] Re: vlookup in R

[Ben Fairbank]

Quite right, there is an optional 4th argument, and the table must be
sorted ascending on the first column in Excel.  Thus these functions
only approximately duplicate the Excel functions (improve on them IMHO).

BTW, I pasted the wrong formula in my reply; though it works, simpler is

ID <- 4      #for example, find value corresponding to 4

x[x[,1]==ID,2]

Ben 

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of David Winsemius
Sent: Monday, March 24, 2008 10:20 AM
To: r-help at stat.math.ethz.ch
Subject: [PS] Re: [R] vlookup in R

Sachin J <sachinj.2006 at yahoo.com> wrote in
news:897147.50760.qm at web37606.mail.mud.yahoo.com: 

> Is there are function similar to excel vlookup in R. Please let me
> know. 
> 
Caveat: definition of VLOOKUP done from memory and by checking OO.o 
Calc function of same name. (Don't have Excel on this machine.)

VLOOKUP looks up a single value in the first column of an Excel range 
and returns a column value (offset by a given integer) from the first 
matching row in that "range". The indexing functions ("extract" or 
"[" ) can be used:

> df4
     V1 V2  V3
1  4.56  1 0.1
2  8.42  1 0.2
3  0.79  3 0.3
4  5.39  3 0.4
5  0.95  4 0.5
6  7.73  5 0.6
7  7.17  6 0.7
8  3.89  7 0.8
9  0.54 10 1.0
10 9.53  9 0.9

> df4[df4$V1==0.79,2]
[1] 3

vlookup <- function(val, df, row){
               df[df[1] == val, row][1] }

> vlookup(0.79, df4, 2)
[1] 3

I thought there was an optional 4th argument to VLOOKUP that specifies 
the action to be taken if there is no exact match. You may need to 
change the equality in that function to an inequality and identify the 
first column value that is less than or equal to "val". If I remember 
correctly, Excel assumes that the first column is ordered ascending.

-- 
David Winsemius

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