# [R] help: selection of data

jim holtman jholtman at gmail.com
Sat Oct 25 19:38:33 CEST 2008

```If you only want the first sequence, then this might work:

> x <- c(-10, -5, 0, 5, 10, 15, 20)
> y <- c(10, 10, 10, -5, -6, -7, 10)
> data <- as.matrix( cbind(x, y) )
> # if you only want the first 'run', then use 'rle' to find it
> mask <- data[,1] > 0 & data[,2] > min(data[,2])
> # now either the first or second will be TRUE, so find it
> offset <- cumsum(c(1, run\$lengths))  # off set of the start of sequence
> index <- if (run\$values) 1 else 2
> new_data <- data[seq(from=offset[index], length=run\$lengths[index]),]
>
> new_data
x  y
[1,]  5 -5
[2,] 10 -6
> data
x  y
[1,] -10 10
[2,]  -5 10
[3,]   0 10
[4,]   5 -5
[5,]  10 -6
[6,]  15 -7
[7,]  20 10

On Sat, Oct 25, 2008 at 12:33 PM, Martin Ballaschk <qcumba at web.de> wrote:
> Hi,
>
> I'm not very experienced with R and struggle with data selection from a long
> matrix with two columns.
>
> I want to cut out the data between x > 0 and min(y).
>
>> x <- c(-10, -5, 0, 5, 10, 15, 20)
>> y <- c(10, 10, 10, -5, -6, -7, 10)
>> data <- as.matrix( cbind(x, y) )
>
>> data
>       x  y
> [1,] -10 10
> [2,]  -5 10
> [3,]   0 10 _
> [4,]   5 -5  |-- data interval
> [5,]  10 -6 _|   to be selected
> [6,]  15 -7
> [7,]  20 10
>
>
> I need that to select the interval between a time 0 and a peak that is the
> minimum here to fit that interval via nls() later.
>
> Can anybody help? I would be very thankful for general hints how to select
> data with the help of conditions.
>
> Cheers
> Martin
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> and provide commented, minimal, self-contained, reproducible code.
>

--
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?

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