Obtaining geom_line values at mid-month for unequally spread geom_points

Question

I need to obtain value at 15th of every month from the geom line created using the reproducible example below. The original geom points are at varied monthly dates depending on data collection days. Appreciate any help possible enter image description here

Value <- c(19.14104, 11.72115, 9.66083, 10.99109, 13.65047, 10.10627, 13.53027, 18.25272, 25.57741)
Dates <- c("07/11/19", "28/11/19", "16/12/19", "10/01/20", "21/01/20", "03/02/20", "04/03/20", "19/03/20", "20/05/20")

df <- data.frame(Value, Dates)
View(df)

df$Dates <- lubridate::dmy(df$Dates)


gpp_plot <- ggplot() + 
  geom_point(data = df, aes(x=Dates, y=Value), alpha=0.5) +
  geom_line(data = df, aes(x=Dates, y=Value), alpha=0.5) +
  theme(axis.text.y=element_text(size=10),
        axis.title=element_text(size=10, , face = "bold"),
        axis.text.x = element_text(size=10, face = "bold", angle = 45, vjust = 0.5))+
  xlab('') +
  ylab('LI-7810_FCH4_DRY_[nmol+1m-2s-1]') +
  scale_x_date(date_labels = "%b %y",breaks = "1 months") +
  theme(legend.position="none")
gpp_plot

Please include some sample data so your code can be run. https://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example — Jon Spring, Mar 12 '22 at 23:13
Thanks Jon; Let me show some sample data here; I have use lubridate to change to a date format in R. Rest is basic code - I need the value of the geom line at every 15th of the month rather than the original geom points. — SamV, Mar 13 '22 at 15:14
Thats what dput gave me above for the head(data) copied above — SamV, Mar 13 '22 at 15:20

score 1 · Accepted Answer · answered Mar 14 '22 at 07:43

As suggested in comments, you could approx the Value at new dates:

library(ggplot2)
library(lubridate)

Dates <- dmy(Dates)

NewDates <- seq(floor_date(min(Dates),'month'),floor_date(max(Dates),'month'),by='month')+days(14)

#[1] "2019-11-15" "2019-12-15" "2020-01-15" "2020-02-15" "2020-03-15" "2020-04-15" "2020-05-15"

NewValue <- approx(Dates,Value,NewDates)$y

df <- data.frame(Value=c(Value,NewValue), Dates=c(Dates,NewDates))


gpp_plot <- ggplot() + 
  geom_point(data = df, aes(x=Dates, y=Value), alpha=0.5) +
  geom_line(data = df, aes(x=Dates, y=Value), alpha=0.5) +
  theme(axis.text.y=element_text(size=10),
        axis.title=element_text(size=10, , face = "bold"),
        axis.text.x = element_text(size=10, face = "bold", angle = 45, vjust = 0.5))+
  scale_x_date(date_labels = "%b %y",breaks = "1 months") +
  ylab('LI-7810_FCH4_DRY_[nmol+1m-2s-1]') +

  theme(legend.position="none")
gpp_plot

Thanks! -- is there a way to add spline instead of a line in the above approx function. I did not seem to find method ='spline' for the above function. do you recommend any work around? — SamV, May 18 '22 at 10:40

Obtaining geom_line values at mid-month for unequally spread geom_points

1 Answers1