Speed up the analysis - performance

Question

I have 2 dataframes in R for example df and dfrefseq.
df<-data.frame( chr = c("chr1","chr1","chr1","chr4")
, start = c(843294,4329248,4329423,4932234)
, stop = c(845294,4329248,4529423,4935234)
, genenames= c("HTA","OdX","FEA","MGA")
)
dfrefseq<-data.frame( chr = c("chr1","chr1","chr1","chr2")
, start = c(843294,4329248,4329423,4932234)
, stop = c(845294,4329248,4529423,4935234)
, genenames= c("tra","FGE","FFs","FAA")
)
I want to check for each gene in df witch gene in dfrefseq lies closest to the selected df gene.
I first selected "chr1" in both dataframes.
Then I calculated for the first gene in readschr1 the distance between start-start start-stop stop-start and stop-stop sites.
The sum of this calculations say everything about the distance. My question here is, How can I speed up this analyse? Because now I tested only 1 gene against a dataframe, but I need to test 2000 genes.
readschr1 <- subset(df,df[,1]=="chr1")
refseqchr1 <- subset(dfrefseq,dfrefseq[,1]=="chr1")
names<-list()
read_start_start<-list()
read_start_stop<-list()
read_stop_start<-list()
read_stop_stop<-list()
for (i in 1:nrow(refseqchr1)) {
startstart<-abs(readschr1[1,2] - refseqchr1[i,2])
startstop<-abs(readschr1[1,2] - refseqchr1[i,3])
stopstart<-abs(readschr1[1,3] - refseqchr1[i,2])
stopstop<-abs(readschr1[1,3] - refseqchr1[i,3])
read_start_start[[i]]<- matrix(startstart)
read_start_stop[[i]]<- matrix(startstop)
read_stop_start[[i]]<- matrix(stopstart)
read_stop_stop[[i]]<- matrix(stopstop)
names[[i]]<-matrix(refseqchr1[i,4])
}
table<-cbind(names, read_start_start, read_start_stop, read_stop_start, read_stop_stop)
sumtotalcolumns<-as.numeric(table[,2]) + as.numeric(table[,3])+ as.numeric(table[,4]) + as.numeric(table[,5])
test<-cbind(table, sumtotalcolumns)
test1<-test[order(as.vector(test$sumtotalcolumns)), ]
Thank you!

Answer 1

The Bioconductor package GenomicRanges is designed to work with this type of data
source('http://bioconductor.org/biocLite.R')
biocLite('GenomicRanges') # one-time installation
then
library(GenomicRanges)
gr <- with(df,
GRanges(factor(chr, levels=paste("chr", 1:4, sep="")),
IRanges(start, stop), genenames=genenames))
grrefseq <- with(dfrefseq,
GRanges(factor(chr, levels=paste("chr", 1:4, sep="")),
IRanges(start, stop), genenames=genenames))
and
> nearest(gr, grrefseq)
[1] 1 2 3 NA

Answer 2

You can merge the two separate data.frames together to form one table and then use vectorized operations. The key to merge is to specify the common column(s) between the data.frames and to tell it what to do when there are cases that do not match. Specifying all = TRUE will return all rows and fill in NAs if there is no match in the other data.frame, i.e. ch2 and ch4 in this case. Once the data.frames have been merged, then it's a simple exercise in subtracting the different columns from one another and then summing the four columns of interest. I use transform to cut down on the typing needed to do the subtraction.
zz <- merge(df, dfrefseq, by = "chr", all = TRUE)
zz <- transform(zz,
read_start_start = abs(start.x - start.y)
, read_start_stop = abs(start.x - stop.y)
, read_stop_start = abs(stop.x - start.y)
, read_stop_stop = abs(stop.x - stop.y)
)
zz <- transform(zz,
sum_total_columns = read_start_start + read_start_stop + read_stop_start + read_stop_stop
)
Here's one approach get the row with the minimum distance. I'm assuming you want to do this by chr and genenames. I use the plyr package, but I'm sure there are base solutions if you'd prefer one of those. Maybe someone else will chime in with a base solution.
require(plyr)
ddply(zz, c("chr", "genenames.x"), function(x) x[which.min(x$sum_total_columns) ,])