CODEWITHSUNDEEP
r
MJL
MJL

Reputation: 301

Label every nth datapoint in ggplot

I am wanting to plot changes in weight(X) per day(Y). I would like to label the very first datapoint, then every seventh.

I am currently using geom_point() + geom_label(aes(label = weight)). I was thinking maybe rep() would do this, but I can't figure out how; if it even will.

Upvotes: 1

Views: 1570

Answers (2)

Jon Spring
Jon Spring

Reputation: 66825

my_data = data.frame(timecount = 1:210,
                     value = 1:210 + 20*sin((1:30)/10))

library(dplyr); library(ggplot2)

my_data %>%
  ggplot(aes(timecount, value)) +
  geom_point()

enter image description here

my_data %>%
  mutate(row = row_number()) %>%
  filter(row %% 7 == 1) %>%   # modulo operator: only keep rows
                              # where the remainder of row / 7 is 1,
                              # i.e.  1, 8, 15, etc.
  ggplot(aes(timecount, value)) +
  geom_point()

enter image description here

Upvotes: 0

neilfws
neilfws

Reputation: 33792

You can pass the data to geom_label and filter for row numbers that match your condition.

Assuming that by "every seventh" you mean 7, 14, 21... use %% 7 == 0. Otherwise use %% 7 == 1 for 8, 15, 22...

library(dplyr)
library(ggplot2)

mydata <- data.frame(x = 2 * (1:49), 
                     y = 3 * (1:49))

mydata %>% 
  ggplot(aes(x, y)) + 
  geom_point() + 
  geom_label(aes(label = x), 
             data = . %>% 
               filter(row_number() %% 7 == 0 | row_number() == 1))

Result:

enter image description here

Upvotes: 4

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