[R] Optimize code to read text-file with digits

[PIKAL Petr]

Hi

see in line


> -----Original Message-----
> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Martin
> Moller Skarbiniks Pedersen
> Sent: Friday, September 8, 2017 11:58 AM
> To: r-help at r-project.org
> Subject: Re: [R] Optimize code to read text-file with digits
>
> On 8 September 2017 at 11:25, PIKAL Petr <petr.pikal at precheza.cz> wrote:
>
> > > Moller Skarbiniks Pedersen
>
> > My program which is slow looks like this:
> > >
> > > filename <- "digits.txt"
> > > lines <- readLines(filename)
> >
> > why you do not read a file as a whole e.g. by
> >
> > lines<-read.table("digits.txt")
> >
>
> Good idea.
>
> >
> > And now I am lost.
>
>
> [...]
>
>
> >  Or do you want one big numeric vector from all your numbers?
>
> here you need to read values as character variables
> >
>
> Yes. That's what I am looking for.

*********************

Well, this is how you cen get your numeric vector of length 1e6

set.seed(111)
numbers0<-sample(0:9, 1e6, replace=TRUE)

If you want to get this number vector from the file it is better to use lists and lapply but maybe with loop it can be done too

First I prepare some data>

daf<-as.character(numbers0)
index<- 0:(1e6-1)
index<-index%/%5
lll<-split(daf, index)
lll<-lapply(lll, paste, collapse="")
daf<-do.call(rbind, lll)
dim(daf)<-c(20000,10)
daf<-as.data.frame(daf)

# here we have data frame similar to what you can get with read.table
head(daf)
     V1    V2    V3    V4    V5    V6    V7    V8    V9   V10
1 57353 75381 66866 52351 03707 13763 76897 67383 02972 37636
2 40540 52811 02521 18199 23236 64967 70123 46962 95347 47379
3 55001 55094 36922 08811 77704 99060 65902 28279 29131 98979
4 41936 77976 71345 84996 36865 11825 11024 90616 35653 10772
5 42339 89821 23790 62176 03266 36054 34882 06822 10087 05317
6 36275 45199 80796 54458 38836 87953 64394 02685 25788 19502
>
# now it is time transform data.frame to numeric vector
# Change to list, transform to character, split to items, unlist and make numeric
lll<- as.list(daf)
lll<-lapply(lll, as.character)
numbers<-lapply(lll, strsplit,"")
numbers <- as.numeric(unlist(numbers))
length(numbers)
[1] 1000000
> all.equal(numbers, numbers0)
[1] TRUE
>
all this is computed in less than 1 second, is it really so slow?

Cheers
Petr

******************


>
> >
> > lines<-read.table("digits.txt", colClasses="character")
> > numbers<-as.numeric(unlist(strsplit(as.character(lines[1,]),"")))
> > changes first row to numeric vector.
> >
> >
> Do I still need to loop through all lines?
> It is maybe even slower now.
>
> numbers <- vector('numeric')
> for (i in 1:nrows(lines)) {
>   numbers <- c(numbers, as.numeric(unlist(strsplit(as.
> character(lines[i,]),""))))
> }
>
>
> > Anyway, can you explain what is your final goal?
> >
> >
> A numeric vector of length 1 million. Each element should be one digit.
>
>
> > Cheers
> > Petr
> >
> >
> Thanks.
> /Martin
>
>       [[alternative HTML version deleted]]
>
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