r - Split dataframe into two groups -

i've simulated data.frame:

library(plyr); library(ggplot2) count <- rev(seq(0, 500, 20)) tide <- seq(0, 5, length.out = length(count)) df <- data.frame(count, tide)  count_sim <- unlist(llply(count, function(x) rnorm(20, x, 50))) count_sim_df <- data.frame(tide=rep(tide,each=20), count_sim) 

and can plotted this:

ggplot(df, aes(tide, count)) + geom_jitter(data = count_sim_df, aes(tide, count_sim), position = position_jitter(width = 0.09)) + geom_line(color = "red") 

i want split count_sim_df 2 group: high , low. when plot split count_sim_df, should (everything in green , blue photoshopped). bit i'm finding tricky getting overlap between high , low around middle values of tide.

this how want split count_sim_df high , low:

• assign half of count_sim_df high , half of count_sim_df low
• reassign values of count create overlap between high , low around middle values of tide

here's way generate sample dataset , groupings using relatively little code , base r:

library(ggplot2) count <- rev(seq(0, 500, 20)) tide <- seq(0, 5, length.out = length(count)) df <- data.frame(count, tide)  count_sim_df <- data.frame(tide = rep(tide,each=20),                            count = rnorm(20 * nrow(df), rep(count, each = 20), 50)) margin <- 0.3 count_sim_df$`tide level` <-   with(count_sim_df,     factor((tide >= quantile(tide, 0.5 + margin / 2) |            (tide >= quantile(tide, 0.5 - margin / 2) & sample(0:1, length(tide), true))),            labels = c("low", "high"))) ggplot(df, aes(x = tide, y = count)) +   geom_line(colour = "red") +   geom_point(aes(colour = `tide level`), count_sim_df, position = "jitter") +   scale_colour_manual(values = c(high = "green", low = "blue"))