[R] Slow update(insert) on Data.frame

[Charles C. Berry]

On Tue, 23 Nov 2010, Joel wrote:

>
> Hi
>
> When I try to update an number in a large data.frame by its pos It's really
> slow it take almost a sec to do this and I wonder why and if where is any
> faster way to update a number in a data.frame
>
> ive tried
>
> DF$col[POS]<-number
> DF[xPOS,yPOS]<-number

See

 	?tracemem

then try

 	tracemem( DF )
 	DF$col[POS]<-number
 	DF[xPOS,yPOS]<-number

then
 	mat <- as.matrix( DF )
 	tracemem( mat )
 	mat[ 2,3 ] <- 4
 	mat[ 15 ] <- 5

If your data.frame can be represented by a matrix, a single update will 
likely be faster as it can be done without making any copies.

If you are doing more than one update, it will help to do them all at 
once. Reread

 	?Subscript

and section 5.2 and 5.3 of Intro to R if you are unsure how to do that.

HTH,

Chuck

>
> Thx
> //Joel
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Charles C. Berry                            Dept of Family/Preventive Medicine
cberry at tajo.ucsd.edu			    UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/  La Jolla, San Diego 92093-0901