Cfrgtkky

I have a data frame with a Date column and a column of calculated concentrations of a parameter. I am trying to plot a time-series plot that has scatter points of all the concentrations and then have a horizontal line showing the standard of the pollutant(which is 500). I can do this no problem. The problem I am having is trying to plot a line showing the duration of the exceedances > 500. I can't seem to find anything to solve my question. I would appreciate any guidance.

Sample Data:

df<-structure(list(Date_Time = structure(c(1480093200, 1482660000, 

1395651343, 1329823800, 1326929400, 1331233200, 1490130000, 1476138600, 

1474070400, 1489393800, 1483272000, 1393515068, 1480471200, 1332680400, 

1471226400, 1470853800, 1396124591, 1496250000, 1394581991, 1438177553, 

1332108000, 1493051400, 1475949600, 1491024600, 1488832200, 1473697800, 

1475404200, 1488511800, 1490212800, 1477040400, 1494793740, 1389346885, 

1473933600, 1390611191, 1486551600, 1476475200, 1473593400, 1388854543, 

1327012200, 1493611140), class = c("POSIXct", "POSIXt"), tzone = "UTC"), 

    Calculated_TDS = c(271.3692, 634.3604, 634.246, 219.546, 

    674.286, 169.21, 506.118, 452.6932, 314.8412, 4640.3052, 

    358.0844, 734.918, 97.71, 460.358, 385.998, 283.9532, 370.554, 

    309.2356, 296.766, 137.079616, 24.494, 383.996, 321.2476, 

    784.6248, 642.1396, 1320.7032, 213.254, 462.1884, 547.6452, 

    376.274, 195.1216, 595.35, 320.1608, 411.166, 882.5512, 288.5292, 

    533.574, 1000.326, 124.022, 256.6116)), row.names = c(NA, 

-40L), class = c("tbl_df", "tbl", "data.frame"), .Names = c("Date_Time", 

"Calculated_TDS"))

Code:

library(tidyverse)



test_df<-df%>%

    mutate(greater = Calculated_TDS > 500)%>%

    group_by(Date_Time,Calculated_TDS)%>%

    summarize(n_greater = sum(greater), duration = length(Date_Time))





plot<-ggplot() +

  geom_point(data = test_df , aes(x = Date_Time, y = Calculated_TDS))+

  geom_line(data= test_df,aes(x=Date_Time, y = duration),stat="identity")+

  geom_hline(aes(yintercept = 500,color="red"),size=1.3)



plot

I know what I have doesn't make sense but I don't understand how to find the duration of exceedances.

Andrew Lavers' answer is a good one. An alternative approach is to make groups for your geom_line and subset data within that geom.

test_df$group <- paste0("Group_", cumsum(c(1, diff(test_df$n_greater) != 0)))

test_df$duration <- ifelse(test_df$n_greater == 1, diff(test_df$Date_Time), 0)



# A tibble: 40 x 5

# Groups:   Date_Time [?]

   Date_Time           Calculated_TDS n_greater duration group  

   <dttm>                       <dbl>     <int>    <dbl> <chr>  

 1 2012-01-18 23:30:00          674.          1      23  Group_1

 2 2012-01-19 22:30:00          124.          0       0  Group_2

 3 2012-02-21 11:30:00          220.          0       0  Group_2

 4 2012-03-08 19:00:00          169.          0       0  Group_2

 5 2012-03-18 22:00:00           24.5         0       0  Group_2

 6 2012-03-25 13:00:00          460.          0       0  Group_2

 7 2014-01-04 16:55:43         1000.          1     137. Group_3

 8 2014-01-10 09:41:25          595.          1     351. Group_3

 9 2014-01-25 00:53:11          411.          0       0  Group_4

10 2014-02-27 15:31:08          735.          1     296. Group_5

# ... with 30 more rows



ggplot() +

  geom_point(data = test_df , aes(x = Date_Time, y = Calculated_TDS))+

  geom_line(data = subset(test_df, Calculated_TDS > 500), aes(x=Date_Time, y = Calculated_TDS, group = group), stat="identity")+

  geom_hline(aes(yintercept = 500,color="red"),size=1.3)

I am not quite sure what you want, but here is a starting point. The idea is simply to make columns for the exceeded and the below, filled with NA, and then plot.
Color assigned is red to the the exceeded line and blue to the below points. Note that the color = "red" should be outside the aes for the horizontal line. Only use color inside aes when the color should vary with the value.

library(tidyverse)

test_df <- df %>% 

  mutate(greater = Calculated_TDS > 500, 

         exceed_value = if_else(greater, Calculated_TDS, as.numeric(NA)), 

         below_value = if_else(greater, as.numeric(NA), Calculated_TDS))



plot <- ggplot(data = test_df, aes(x = Date_Time)) + 

  geom_point(aes(y = exceed_value),  color = "red") + 

  geom_point(aes(y = below_value), color = "blue") + 

  geom_line(aes(y = exceed_value), 

  color = "red") + geom_hline(aes(yintercept = 500), color = "red", size = 1.3)



print(plot)

#> Warning in as.POSIXlt.POSIXct(x): unknown timezone 'zone/tz/2018g.1.0/

#> zoneinfo/America/New_York'

#> Warning: Removed 26 rows containing missing values (geom_point).

#> Warning: Removed 14 rows containing missing values (geom_point).

#> Warning: Removed 4 rows containing missing values (geom_path).