I have the following data in R: 

```
id <- factor(seq(1:72))
initial.e <- rnorm(n=72, mean = 21.51, sd = 6.58)
initial.f <- rnorm(n = 72, mean = 20.75, sd = 3.378)

final.e <- rnorm(n = 72, mean = 19.81, sd = 7.48)
final.f <- rnorm(n = 72, mean = 19.77, sd = 5.389)

data <- data.frame(id,initial.e, initial.f, final.e, final.f)

```

I need to create a scatter plot with two straight trendlines for `e` and `f`, but I'm lost on how to create that. I found this article: <https://sakaluk.wordpress.com/2015/08/27/6-make-it-pretty-plotting-2-way-interactions-with-ggplot2/> which I tried following, but didn't work the way I wanted. 

I also tried using `melt` from `reshape2` package, but I can't get the plots to show the way I want to - with two trendlines for `e` and `f` in the scatter plot. 

```
datamelt <- melt(data, id = 'id')
datamelt <- datamelt %>% mutate(names = ifelse(datamelt$variable %in% c('initial.e', 'initial.f'), 'Before', 'After'))

datamelt <- datamelt %>% mutate(types = ifelse(datamelt$variable %in% c('final.e', 'final.f'), 'e', 'f'))

```

After this things went downhill. All the codes I tried either have some basic scatter plot with `geom_smooth()` or just some generic error. 

**EDIT**

The plot should contain scatterplot containing relationship between `intial.e` and `initial.f` with a trend line, and another relationship between `final.e` and `final.f` with a trend line in the same plot.