# [R] Random selection of a fixed number of values by interval

Frank S. f_j_rod at hotmail.com
Tue Dec 15 10:27:39 CET 2015

```Many thanks to David L Carlson, Ben Gunter and David Winsemius for your quick and very elegant solutions!!
With your  list answers I am learning sa lot of things that will help me in the future to program.

Best,

Frank S.

> Subject: Re: [R] Random selection of a fixed number of values by interval
> From: dwinsemius en comcast.net
> Date: Mon, 14 Dec 2015 13:31:45 -0800
> CC: f_j_rod en hotmail.com; r-help en r-project.org
> To: dcarlson en tamu.edu
>
>
> > On Dec 14, 2015, at 12:46 PM, David L Carlson <dcarlson en tamu.edu> wrote:
> >
> > There are lots of ways to do this. For example,
>
> Another method with mapply:
>
>  mapply(function( n, vals) {sample(vals\$id, n)} ,   # no replacement is the default for sample
>             vals= split(data, findInterval(data\$value, 0:5) )[1:5] , # drops the values at 5 or above
>             n=c(10,7,5,5,3)   )
>
> \$`1`
>  [1] 12 64 10 60 70 58 33 50 57 68
>
> \$`2`
> [1] 43  8 15 26 19  3 20
>
> \$`3`
> [1] 55  9 62 17 67
>
> \$`4`
> [1] 61 21 31 24 48
>
> \$`5`
> [1] 44 13 36
>
> >
> >> groups <- cut(data\$value, include.lowest = T, right = FALSE,
> > +      breaks = 0:ceiling(max(data\$value)))
> >> grp <- c("[0,1)", "[1,2)", "[2,3)", "[3,4)", "[4,5)")
> >> size <- c(10, 7, 5, 5, 3)
> >> set.seed(42)
> >> samples <- lapply(1:5, function(x) sample(data\$id[groups==grp[x]],
> > +      size[x]))
> >> names(samples) <- grp
> >> samples
> > \$`[0,1)`
> > [1] 69 68 33 63 56 46 65 12 50 58
> >
> > \$`[1,2)`
> > [1] 20 34 43  8 15 52 19
> >
> > \$`[2,3)`
> > [1]  7 22 62 28  2
> >
> > \$`[3,4)`
> > [1] 61 53  5 25 21
> >
> > \$`[4,5)`
> > [1] 59 35 40
> >
> >>
> >> groups <- cut(data\$value, include.lowest = T, right = FALSE,
> > +      breaks = 0:ceiling(max(data\$value)))
> >> grp <- c("[0,1)", "[1,2)", "[2,3)", "[3,4)", "[4,5)")
> >> size <- c(10, 7, 5, 5, 3)
> >> set.seed(42)
> >> samples <- lapply(1:5, function(x) sample(data\$id[groups==grp[x]],
> > +      size[x]))
> >> names(samples) <- grp
> >> samples
> > \$`[0,1)`
> > [1] 69 68 33 63 56 46 65 12 50 58
> >
> > \$`[1,2)`
> > [1] 20 34 43  8 15 52 19
> >
> > \$`[2,3)`
> > [1]  7 22 62 28  2
> >
> > \$`[3,4)`
> > [1] 61 53  5 25 21
> >
> > \$`[4,5)`
> > [1] 59 35 40
> >
> >
> > -------------------------------------
> > David L Carlson
> > Department of Anthropology
> > Texas A&M University
> > College Station, TX 77840-4352
> >
> >
> >
> > -----Original Message-----
> > From: R-help [mailto:r-help-bounces en r-project.org] On Behalf Of Frank S.
> > Sent: Monday, December 14, 2015 2:02 PM
> > To: r-help en r-project.org
> > Subject: [R] Random selection of a fixed number of values by interval
> >
> > Dear R users,
> >
> > I'm writing to this list because I must get a random sample (without replacement) from a given vector, but the clue is that I need to extract a fixed number of values by each prespecified 1-unit interval. As an example I try to say, I have a data frame that looks like this (my real dataframe is bigger):
> >
> > data <- data.frame(id = 1:70, value=  c(0.68, 2.96, 1.93, 5.63, 3.08, 3.10, 2.99, 1.79, 2.96, 0.85, 11.79, 0.06, 4.31, 0.64, 1.43, 0.88, 2.79, 4.67,
> >      1.23, 1.43, 3.05, 2.44, 2.55, 3.82, 3.55, 1.56, 7.25, 2.75, 9.64, 5.14, 3.54, 3.12, 0.17, 1.07, 4.08, 4.47, 5.58, 7.41, 0.85, 4.30, 7.58,
> >      0.58, 1.40, 4.74, 5.04, 0.14, 1.14, 3.28, 7.84, 0.07, 3.97, 1.02, 3.47, 0.66, 2.38, 0.06, 0.67, 0.48, 4.48, 0.12, 3.82, 2.27, 0.93, 0.30,
> >      0.73, 0.33, 2.91, 0.81, 0.18, 0.42))
> >
> > And I would like to select, in a random manner:
> >
> > 10 id's whose value belongs to [0,1) interval
> > 7 id's whose value belongs to [1,2)
> > 5 id's whose value belongs to [2,3)
> > 5 id's whose value belongs to [3,4)
> > 3 id's whose value belongs to [4,5)
> >
> > # I have the following values by each 1-unit interval:
> > table(cut(data\$value, include.lowest = T, right = FALSE, breaks = 0:ceiling(max(data\$value))))
> >
> > and the size vector:
> > size <- c(10, 7, 5, 5, 3)
> >
> > But I'm not able to get it by using sample function. Does anyone have some idea?
> >
> > Thank you very much for any suggestions!!
> >
> > Frank S.
> >
> >
> >
> >
> >
> > 	[[alternative HTML version deleted]]
> >
> > ______________________________________________
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> > and provide commented, minimal, self-contained, reproducible code.
> >
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