[R] Secondary y axis in ggplot2: did not respond when change its y-axis value

[Thierry Onkelinx]

The second y-axis in ggplot2 is only intended to relabel an axis with a
fixed transformation. E.g. one axis in degree Celcius and one in Kelvin,
km and miles, ...
It does not rescale the variables.

It looks like you want to display two variables with unrelated units on the
same y-axis. That is not a good idea. https://blog.datawrapper.de/dualaxis/

ir. Thierry Onkelinx
Statisticus / Statistician

Vlaamse Overheid / Government of Flanders
INSTITUUT VOOR NATUUR- EN BOSONDERZOEK / RESEARCH INSTITUTE FOR NATURE AND
FOREST
Team Biometrie & Kwaliteitszorg / Team Biometrics & Quality Assurance
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Op vr 8 jan. 2021 om 02:02 schreef Marna Wagley <marna.wagley using gmail.com>:

> Hi R users,
> I was trying to plot a graph with a secondary axis, and used the following
> code for the data but the secondary line and secondary y -axis value did
> not match. I would like to show both lines in one graph.
>
> Any suggestions?
>
> library(ggplot2)
> library(reshape2)
> daT<-structure(list(x = c(1L, 2L, 3L, 4L, 5L, 6L, 7L, 8L, 1L, 2L,
> 3L, 4L, 5L, 6L, 7L, 8L), y1 = c(9754L, 1051L, 5833L, 5769L, 2479L,
> 470L, 5828L, 174L, 2045L, 6099L, 8780L, 8732L, 4053L, 9419L,
> 4728L, 3587L), y2 = c(0.51, 0.61, 0.3, 0.81, 0.89, 0, 1.9, 0.76,
> 0.87, 0.29, 0, 0.42, 0.73, 0.96, 0.62, 0.06), group = c("A",
> "A", "A", "A", "A", "A", "A", "A", "B", "B", "B", "B", "B", "B",
> "B", "B")), class = "data.frame", row.names = c(NA, -16L))
> print(daT)
> daT1<-melt(daT, id.vars=c("x", "group"))
> daT1%>%
>   ggplot() +
>   geom_line(aes(x = x, y = value, group = variable, color = variable)) +
>   facet_wrap(~group) +
>   scale_y_continuous(sec.axis = sec_axis(~ .*0.0001))
>
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>
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