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

-----Original Message-----
From: POLWART, Calum (COUNTY DURHAM AND DARLINGTON NHS
FOUNDATION TRUST) <calum.polwart at nhs.net>
Sent: Thursday, January 17, 2019 2:56 PM
To: PIKAL Petr <petr.pikal at precheza.cz>; Ben Tupper <btupper at bigelow.org>
Cc: r-help at r-project.org
Subject: RE: [R] I can't get seq to behave how I think it should

Thanks guys.

I've used Petr's method and its working for me.

If the data had been from a calculation I'd have rounded it... just didn't expect
seq to break it!

C

-----Original Message-----
From: PIKAL Petr [mailto:petr.pikal at precheza.cz]
Sent: 17 January 2019 13:53
To: Ben Tupper; POLWART, Calum (COUNTY DURHAM AND DARLINGTON NHS
FOUNDATION TRUST)
Cc: r-help at r-project.org
Subject: RE: [R] I can't get seq to behave how I think it should

Hi

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

Cheers
Petr

-----Original Message-----
From: R-help <r-help-bounces at 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 at nhs.net>
Cc: r-help at 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 at 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?

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