Reputation: 2067

ggplot add average line to specific months facet

I am trying to add an "average" line for the month "3" for each year of time series ggplot plots that I have.

I want to draw a horizontal line through the average of the facets - I have tried group_by, mutate etc. but cannot get it working.

Expected output would be just a horizontal line through each of the facets based on that facets months "3" average value.

Code:

dat %>% 
  ggplot(aes(x = day, y = NO2)) +
  geom_line() +
  facet_grid(~year)

Data:

dat <- structure(list(station_location = c("Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen", "Pza del Carmen", "Pza del Carmen", "Pza del Carmen", 
"Pza del Carmen"), date = structure(c(16495, 16496, 16497, 16498, 
16499, 16500, 16501, 16502, 16503, 16504, 16505, 16506, 16507, 
16508, 16509, 16510, 16511, 16512, 16513, 16514, 16515, 16516, 
16517, 16518, 16519, 16520, 16521, 16522, 16523, 16524, 16525, 
16861, 16862, 16863, 16864, 16865, 16866, 16867, 16868, 16869, 
16870, 16871, 16872, 16873, 16874, 16875, 16876, 16877, 16878, 
16879, 16880, 16881, 16882, 16883, 16884, 16885, 16886, 16887, 
16888, 16889, 16890, 16891, 17226, 17227, 17228, 17229, 17230, 
17231, 17232, 17233, 17234, 17235, 17236, 17237, 17238, 17239, 
17240, 17241, 17242, 17243, 17244, 17245, 17246, 17247, 17248, 
17249, 17250, 17251, 17252, 17253, 17254, 17255, 17256, 17591, 
17592, 17593, 17594, 17595, 17596, 17597, 17598, 17599, 17600, 
17601, 17602, 17603, 17604, 17605, 17606, 17607, 17608, 17609, 
17610, 17611, 17612, 17613, 17614, 17615, 17616, 17617, 17618, 
17619, 17620, 17621, 17956, 17957, 17958, 17959, 17960, 17961, 
17962, 17963, 17964, 17965, 17966, 17967, 17968, 17969, 17970, 
17971, 17972, 17973, 17974, 17975, 17976, 17977, 17978, 17979, 
17980, 17981, 17982, 17983, 17984, 17985, 17986), class = "Date"), 
    yvar = c(31, 35, 51, 55, 50, 62, 83, 62, 74, 80, 82, 77, 
    54, 38, 39, 48, 54, 49, 36, 36, 36, 37, 58, 41, 32, 38, 44, 
    57, 40, 54, 69, 70, 57, 48, 45, 35, 33, 39, 46, 46, 43, 50, 
    50, 49, 51, 54, 72, 64, 47, 35, 41, 53, 46, 55, 44, 48, 35, 
    21, 23, 34, 53, 34, 42, 53, 48, 26, 25, 34, 45, 71, 79, 80, 
    59, 31, 30, 43, 44, 45, 58, 65, 59, 43, 33, 29, 37, 50, 48, 
    30, 32, 47, 59, 57, 44, 39, 60, 33, 34, 37, 39, 41, 57, 55, 
    42, 21, 28, 48, 47, 28, 35, 33, 38, 44, 44, 51, 59, 60, 31, 
    39, 55, 47, 47, 28, 20, 30, 56, 49, 34, 13, 22, 16, 18, 34, 
    38, 38, 41, 37, 29, 39, 58, NA, NA, NA, 29, 30, 42, 44, 33, 
    29, 32, 24, 44, 48, 34, 27, 26), year = c(2015L, 2015L, 2015L, 
    2015L, 2015L, 2015L, 2015L, 2015L, 2015L, 2015L, 2015L, 2015L, 
    2015L, 2015L, 2015L, 2015L, 2015L, 2015L, 2015L, 2015L, 2015L, 
    2015L, 2015L, 2015L, 2015L, 2015L, 2015L, 2015L, 2015L, 2015L, 
    2015L, 2016L, 2016L, 2016L, 2016L, 2016L, 2016L, 2016L, 2016L, 
    2016L, 2016L, 2016L, 2016L, 2016L, 2016L, 2016L, 2016L, 2016L, 
    2016L, 2016L, 2016L, 2016L, 2016L, 2016L, 2016L, 2016L, 2016L, 
    2016L, 2016L, 2016L, 2016L, 2016L, 2017L, 2017L, 2017L, 2017L, 
    2017L, 2017L, 2017L, 2017L, 2017L, 2017L, 2017L, 2017L, 2017L, 
    2017L, 2017L, 2017L, 2017L, 2017L, 2017L, 2017L, 2017L, 2017L, 
    2017L, 2017L, 2017L, 2017L, 2017L, 2017L, 2017L, 2017L, 2017L, 
    2018L, 2018L, 2018L, 2018L, 2018L, 2018L, 2018L, 2018L, 2018L, 
    2018L, 2018L, 2018L, 2018L, 2018L, 2018L, 2018L, 2018L, 2018L, 
    2018L, 2018L, 2018L, 2018L, 2018L, 2018L, 2018L, 2018L, 2018L, 
    2018L, 2018L, 2018L, 2018L, 2019L, 2019L, 2019L, 2019L, 2019L, 
    2019L, 2019L, 2019L, 2019L, 2019L, 2019L, 2019L, 2019L, 2019L, 
    2019L, 2019L, 2019L, 2019L, 2019L, 2019L, 2019L, 2019L, 2019L, 
    2019L, 2019L, 2019L, 2019L, 2019L, 2019L, 2019L, 2019L), 
    month = c(3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 
    3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 
    3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 
    3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 
    3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 
    3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 
    3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 
    3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 
    3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 
    3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 
    3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L), day = c(1L, 2L, 3L, 4L, 
    5L, 6L, 7L, 8L, 9L, 10L, 11L, 12L, 13L, 14L, 15L, 16L, 17L, 
    18L, 19L, 20L, 21L, 22L, 23L, 24L, 25L, 26L, 27L, 28L, 29L, 
    30L, 31L, 1L, 2L, 3L, 4L, 5L, 6L, 7L, 8L, 9L, 10L, 11L, 12L, 
    13L, 14L, 15L, 16L, 17L, 18L, 19L, 20L, 21L, 22L, 23L, 24L, 
    25L, 26L, 27L, 28L, 29L, 30L, 31L, 1L, 2L, 3L, 4L, 5L, 6L, 
    7L, 8L, 9L, 10L, 11L, 12L, 13L, 14L, 15L, 16L, 17L, 18L, 
    19L, 20L, 21L, 22L, 23L, 24L, 25L, 26L, 27L, 28L, 29L, 30L, 
    31L, 1L, 2L, 3L, 4L, 5L, 6L, 7L, 8L, 9L, 10L, 11L, 12L, 13L, 
    14L, 15L, 16L, 17L, 18L, 19L, 20L, 21L, 22L, 23L, 24L, 25L, 
    26L, 27L, 28L, 29L, 30L, 31L, 1L, 2L, 3L, 4L, 5L, 6L, 7L, 
    8L, 9L, 10L, 11L, 12L, 13L, 14L, 15L, 16L, 17L, 18L, 19L, 
    20L, 21L, 22L, 23L, 24L, 25L, 26L, 27L, 28L, 29L, 30L, 31L
    )), class = c("tbl_df", "tbl", "data.frame"), row.names = c(NA, 
-155L))

Upvotes: 3

Answers (2)

StupidWolf

Reputation: 46908

You can use geom_smooth, and fit an intercept only line:

dat %>% 
ggplot(aes(x = day, y = yvar)) +
geom_line() +
geom_smooth(method="lm",formula=y~1,se=FALSE)+
facet_grid(~year)

This works because if you fit a linear model, e.g lm(y~1), this is an intercept only model and the intercept will be the mean.

Upvotes: 8

Bertil Baron

Reputation: 5003

you could try something like this

dat %>% 
  group_by(year) %>% 
  mutate(mean = mean(yvar, na.rm = TRUE)) %>%
  ggplot(aes(x = day, y = yvar)) +
  geom_line() + 
  geom_line(aes(y = mean), color = "blue") +
  facet_grid(~year)

what I do is to calculate the mean value for each data point that I have with group_by and mutate. then I add one more geom_line layer but this times I set the y aestetic to be the average value instead of.

Hope this helps!!

Upvotes: 2

ggplot add average line to specific months facet

Answers (2)

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