Using ggplot to map mean values by group

Question

Using an example dataframe:

 df <- structure(list(value = c(10L, 8L, 6L, 4L, 2L, 9L, 7L, 5L, 3L, 
    1L, 1L, 1L, 2L, 3L, 4L, 3L, 3L, 4L, 5L, 2L, 2L, 4L, 6L, 4L, 7L, 
    3L, 5L, 4L, 6L, 3L), length = c(1L, 2L, 3L, 4L, 5L, 1L, 2L, 3L, 
    4L, 5L, 1L, 2L, 3L, 4L, 5L, 1L, 2L, 3L, 4L, 5L, 1L, 2L, 3L, 4L, 
    5L, 1L, 2L, 3L, 4L, 5L), wave = c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 
    1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 3L, 3L, 3L, 
    3L, 3L, 3L, 3L, 3L, 3L, 3L)), .Names = c("value", "length", "wave"
    ), class = c("tbl_df", "tbl", "data.frame"), row.names = c(NA, 
    -30L), spec = structure(list(cols = structure(list(value = structure(list(), class = c("collector_integer", 
    "collector")), length = structure(list(), class = c("collector_integer", 
    "collector")), wave = structure(list(), class = c("collector_integer", 
    "collector"))), .Names = c("value", "length", "wave")), default = structure(list(), class = c("collector_guess", 
    "collector"))), .Names = c("cols", "default"), class = "col_spec"))

I wish to plot the average 'value' (line graph) by 'length' for each group (wave).

Is this possible direct from ggplot? (or do I need to do the preliminary analysis first).

I would have otherwise used:

ggplot(df, aes(x=length, y=value, color=wave)) + geom_point(shape=1)

markus · Accepted Answer · 2018-06-25 10:28:21Z

1

We can use stat_summary for this task

library(ggplot2)
ggplot(df, aes(x = length, y = value, col = as.factor(wave))) + 
  stat_summary(geom = "line", fun.y = mean)

answered Jun 25, 2018 at 10:28

markus

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2 Comments

KT_1 Over a year ago

Thanks @Markus. A few observations when I run my full data. Firstly - my length runs from 1-10. But when I look at the graph it goes 1, 10, 2, 3, 4... is it possible to specify how the numbers run? Secondly the graph doesn't form and I get geom_path: Each group consists of only one observation. Do you need to adjust the group aesthetic? What should I do?

markus Over a year ago

Is your length column a factor by any chance? For the error: try group = factor(wave) inside ggplot(). Above, I used col instead. If still not working, edit your question and use dput() to share your data.

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