How to jitter both geom_line and geom_point by the same magnitude?

On July 2017, developpers of ggplot2 have added a seed argument on position_jitter function (https://github.com/tidyverse/ggplot2/pull/1996).

So, now (here: ggplot2 3.2.1) you can pass the argument seed to position_jitter in order to have the same jitter effect in geom_point and geom_line (see the official documentation: https://ggplot2.tidyverse.org/reference/position_jitter.html)

Note that this seed argument does not exist (yet) in geom_jitter.

ggplot(data = df, aes(x = dimension, y = value,
                      shape = Time, linetype = Time, group = Time)) +
  geom_line(position = position_jitter(width = 0.25, seed = 123)) +
  geom_point(position = position_jitter(width = 0.25, seed = 123)) +
  xlab("Dimension") + ylab("Value")

One solution is to manually jitter the points:

df$value_j <- jitter(df$value)

ggplot(df, aes(dimension, value_j, shape=Time, linetype=Time, group=Time)) +
  geom_line() +
  geom_point() +
  labs(x="Dimension", y="Value")

The horizontal solution for your discrete X axis isn't as clean (it's clean under the covers when ggplot2 does it since it handles the axis and point transformations for you quite nicely) but it's doable:

df$dim_j <- jitter(as.numeric(factor(df$dimension)))

ggplot(df, aes(dim_j, value, shape=Time, linetype=Time, group=Time)) +
  geom_line() +
  geom_point() +
  scale_x_continuous(labels=dimension) +
  labs(x="Dimension", y="Value")

Another option for horizontal only would be to specify position_dodge and pass this to the position argument for each geom.

pd <- position_dodge(0.4)

ggplot(data = df, aes(x = dimension, y = value,
                      shape = Time, linetype = Time, group = Time)) +
  geom_line(position = pd) +
  geom_point(position = pd) +
  xlab("Dimension") + ylab("Value")