Determining the Scale factor for the secondary Y-axis

Question

The dput(Q_Sheet) is below. How can properly introduce a second y-axis that is different in scale from the primary axis?

structure(list(Amino_acids = c(4, 12, 20, 28, 32), Protein_length_Ang = c(7, 
24, 40, 56, 64), length_no_ratio = c(1.75, 2, 2, 2, 2), Corrected_aa = c(1.24459201924769e-12, 
3.71007650662474e-09, 1.10594599229843e-05, 0.0319159404863842, 
0.642857142857143), aa_frequency = c(3.99735380592756, 6.96840672963299, 
4.58228895300999, 3.12310921028256, 4.67560843680985), T_degC = c(50.3857804818545, 
52.8464583426248, 60.0760389538482, 58.1895053328481, 67.628202708438
)), row.names = c(NA, -5L), class = c("tbl_df", "tbl", "data.frame"
), na.action = structure(c(`2` = 2L, `4` = 4L, `6` = 6L), class = "omit"))
`

ggplot(data = Q_Sheet, aes(x = T_degC))+
       geom_line(aes(y = Amino_acids), color="red")+
       geom_line(aes(y = Corrected_aa), color = "blue") + 
scale_y_continuous(name = "Amino_acids", sec.axis = sec_axis(~.*10, name = "Corrected_aa"))

The output is as follows:

     <ScaleContinuousPosition>
 Range:  
 Limits:    0 --    1

Does this answer your question? [Using secondary y-axis in ggplot2 with different scale factor when using facet\_wrap](https://stackoverflow.com/questions/61565304/using-secondary-y-axis-in-ggplot2-with-different-scale-factor-when-using-facet-w) — tjebo, Jul 22 '21 at 10:33
actually I wanted to point to this question here https://stackoverflow.com/questions/3099219/ggplot-with-2-y-axes-on-each-side-and-different-scales — tjebo, Jul 22 '21 at 10:33

score 1 · Answer 1 · answered Jul 22 '21 at 02:23

1

There are two issues - 1) scale_y_continuous typo and 2) there is a missing + connecting the last expression

ggplot(data=Q_Sheet, aes(x=T_degC))+
             geom_line(aes(y=Amino_acids),color="red")+
             geom_line(aes(y=Corrected_aa),color="blue") +
             scale_y_continuous(name="Amino_acids",
        sec.axis=sec_axis(~.*10,name="Corrected_aa"))

-ouptut

answered Jul 22 '21 at 02:23

akrun

874,273
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540
662

Thank you for the correction and help! While it is not advised to have two y-axis, is there a better way to find the correct factor for my secondary y-x scale? – Toy L Jul 22 '21 at 02:32

score 1 · Accepted Answer · answered Jul 22 '21 at 09:35

You can use the below formula to keep the secondary Y-axis at the same level as Corrected_aa.

library(ggplot2)

ggplot(data=Q_Sheet, aes(x=T_degC))+
  geom_line(aes(y=Amino_acids),color="red")+
  geom_line(aes(y=Corrected_aa),color="blue")+
  scale_y_continuous(name="Amino_acids",
                     sec.axis=sec_axis(~{
                       a <- min(Q_Sheet$Corrected_aa)
                       b <- max(Q_Sheet$Corrected_aa)
                       ((((b-a) * (. - min(.)))/diff(range(.))) + a)
                      },name="Corrected_aa"))

score 0 · Answer 3 · answered Jul 22 '21 at 11:03

0

We could define a coefficient and then color the lines to indicate wich lines belongs to which y-scale:

library(ggplot2)

value used to transform the data
coeff <- 0.01

# colors
Amino_acidsColor = "red"
Corrected_aaColor = "blue"

ggplot(data=Q_Sheet, aes(x=T_degC))+
  geom_line(aes(y=Amino_acids), size = 2, color=Amino_acidsColor)+
  geom_line(aes(y=Corrected_aa/coeff), size = 2, color=Corrected_aaColor) +
  scale_y_continuous(name="Amino_acids",
                     sec.axis=sec_axis(~.*coeff,name="Corrected_aa")) +
  theme_bw() +
  theme(
    axis.title.y = element_text(color = Amino_acidsColor, size=13),
    axis.title.y.right = element_text(color = Corrected_aaColor, size=13)
  )

answered Jul 22 '21 at 11:03

TarJae

72,363
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TarJae, how did you know the coef would be 0.010? Is there a formula you used? – Toy L Jul 22 '21 at 22:52
Coeff is arbitrary and up to you which factor you take to transform your data. While you could use the formula used by Ronak or akrun. In my opinion in both cases the corrected_aa y axis does not show the values in detail, which in essence is the job of the second y axis. – TarJae Jul 23 '21 at 05:25

Determining the Scale factor for the secondary Y-axis

3 Answers3