[R] I can't get seq to behave how I think it should

[PIKAL Petr]

Hi

Or you could use rounding.
which(round(lut, 3)==1.8)
[1] 401

Cheers
Petr

> -----Original Message-----
> From: R-help <r-help-bounces using r-project.org> On Behalf Of Ben Tupper
> Sent: Thursday, January 17, 2019 2:43 PM
> To: POLWART, Calum (COUNTY DURHAM AND DARLINGTON NHS
> FOUNDATION TRUST) <calum.polwart using nhs.net>
> Cc: r-help using r-project.org
> Subject: Re: [R] I can't get seq to behave how I think it should
>
> Hi,
>
> This looks like a floating point reality bump - see
>
> https://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-doesn_0027t-R-think-
> these-numbers-are-equal_003f <https://cran.r-project.org/doc/FAQ/R-
> FAQ.html#Why-doesn_0027t-R-think-these-numbers-are-equal_003f>
>
> You can use other methods to finding your row - I would opt for findInterval()
>
> > lut = seq(1.4, 2.1, by=0.001)
> > findInterval(1.8, lut)
> [1] 401
>
> findInterval() uses a rapid search to find the index in the look up table (lut) that
> is just less than  or equal to the search value (in your example 1.8).
>
> Cheers,
> Ben
>
> > On Jan 17, 2019, at 8:33 AM, POLWART, Calum (COUNTY DURHAM AND
> DARLINGTON NHS FOUNDATION TRUST) via R-help <r-help using r-project.org>
> wrote:
> >
> > I am using seq with the expression seq(1.4, 2.1, by=0.001) to create a
> > sequence of references from 1.4 to 2.1 in 0.001 increments.  They
> > appear to be created correctly.  They have a related pair of data
> > which for the purposes of this we will call val.  I'm interested in
> > the content on the row with seq = 1.8. But I can't seem to get it
> > returned.  I can get other values but not 1.8!  yet looking at row 401
> > there is nothing to indicate an issue
> >
> >> a = 1.4
> >> b = 2.1
> >> seq = seq(a, b, by=0.001)
> >> val = ceiling(seq * 50)
> >> s=data.frame(seq, val)
> >> s$val[seq==1.799]
> > [1] 90
> >> s$val[s$seq==1.8]
> > numeric(0)
> >> s$val[seq==1.8]
> > numeric(0)
> >> s$val[s$seq==1.800]
> > numeric(0)
> >> s$val[s$seq==1.801]
> > [1] 91
> >> head(s[s$seq>1.798,])
> >      seq val
> > 400 1.799  90
> > 401 1.800  90
> > 402 1.801  91
> > 403 1.802  91
> > 404 1.803  91
> > 405 1.804  91
> >
> >
> > Can anyone explain what's going on here and how I would correctly find the
> content of row 401 by using an expression to equal the seq column?
> >
> >
> >
> >
> >
> >
> *******************************************************************
> ***
> > **********************************************
> >
> > This message may contain confidential information. If
> > ...{{dropped:25}}
>
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