PaoloH - 6 months ago 24

R Question

So my problem is quite simple, I want to plot the exponential regression of my data, so far what I've done was plot the polynomial regression :

`ggplot(data = mydataANOVA, aes(x = TpsenJour, y = PrptionJourAuDelaDe, color = Type_Contrat))+`

geom_point()+

geom_smooth(method ="lm", formula = y ~ poly(x,2))

I got the following plot :

The regression isn't exactly a good fit for the actual data but the data looked a lot like an exponential function so I used the logarithm of my data, I used the same code with the log of my data to get the following plot:

Which seemed to be an very accurate fit, so I wanted to compare the two regression models directly by plotting the exponential regression, but when i used the formula

`formula = y ~ exp(poly(x,2))`

Which is even less accurate than the first one. How am I supposed to get that polynomial exponential regression plotted with the confidence intervals. I managed to get the good regression on the regular plot function but not with the confidence intervals and not in ggplot2. Here is what I got for only one of the two curves:

How can I get the good regression on ggplot2 with the confidence intervals ?

Here is the data that I used on one of the 2 curves.

`TpsenJour PrptionJourAuDelaDe fact`

1 1 0.955669 a

3 3 0.877947 a

5 5 0.815058 a

7 7 0.764725 a

9 9 0.721070 a

11 11 0.681675 a

13 13 0.646490 a

15 15 0.614689 a

17 17 0.585664 a

19 19 0.558905 a

21 21 0.534362 a

23 23 0.511791 a

25 25 0.490651 a

27 27 0.470923 a

29 29 0.452498 a

31 31 0.435190 a

33 33 0.419160 a

35 35 0.404359 a

37 37 0.390519 a

40 40 0.371018 a

40.1 40 0.371018 a

43 43 0.352960 a

46 46 0.336170 a

49 49 0.320631 a

52 52 0.306194 a

55 55 0.292584 a

58 58 0.279858 a

62 62 0.264096 a

65 65 0.253316 a

68 68 0.243120 a

71 71 0.233544 a

74 74 0.224474 a

77 77 0.215905 a

81 81 0.205180 a

84 84 0.197623 a

87 87 0.190440 a

90 90 0.183609 a

93 93 0.177278 a

96 96 0.171358 a

100 100 0.163951 a

Thank you.

I had a smal problem with the answer of @Roland, where it would return an error, I think I've solved it. I simply had to add two lines : (I hope that by fixing my error I did not alter the originally predicted outcome)

`fact<-DF$fact`

fit <- lm(log(PrptionJourAuDelaDe) ~ poly(TpsenJour, 2) * fact, data = mydataANOVA)

fact<-c(rep('a',1000),rep('b',1000))

pred <- expand.grid(TpsenJour = seq(min(mydataANOVA$TpsenJour), max(mydataANOVA$TpsenJour), length.out = 1e3),

fact = unique(mydataANOVA$fact))

pred <- cbind(pred,

exp(predict(fit,

newdata = data.frame(TpsenJour = pred$TpsenJour),

interval = "confidence")))

ggplot(data = DF, aes(x = TpsenJour, y = PrptionJourAuDelaDe, color = fact)) +

geom_point() +

geom_ribbon(data = pred, aes(y = fit, ymin = lwr, ymax = upr, fill = fact), alpha = 0.3) +

geom_line(data = pred, aes(y = fit, color = fact))

I then get the following plot:

Answer

Do the fit outside of ggplot2:

```
fit <- lm(log(PrptionJourAuDelaDe) ~ poly(TpsenJour, 2) * fact, data = DF)
pred <- expand.grid(TpsenJour = seq(min(DF$TpsenJour), max(DF$TpsenJour), length.out = 1e3),
fact = unique(DF$fact))
pred <- cbind(pred,
exp(predict(fit,
newdata = data.frame(TpsenJour = pred$TpsenJour),
interval = "confidence")))
library(ggplot2)
ggplot(data = DF, aes(x = TpsenJour, y = PrptionJourAuDelaDe, color = fact)) +
geom_point() +
geom_ribbon(data = pred, aes(y = fit, ymin = lwr, ymax = upr, fill = fact), alpha = 0.3) +
geom_line(data = pred, aes(y = fit, color = fact))
```

Note that I wouldn't call this exponential regression. It's linear regression with a transformed dependent variable (in contrast to a non-linear model, which would need to be fitted with `nls`

). And its probably not the model I would use.