Is this behavior of geom_area() strange or am I missing something?-CodePudding

I think I found strange behavior of geom_area() from the ggplot2 package, but before filing an issue at the ggplot2 github site, I wanted to see if I am missing something.

geom_area() produces unexpected weird areas when tiny numbers are added to sane values and the x-axis is on log-scale. I encountered this issue in an ordinary differential equation (ode) simulation setting in systems that have not fully converged yet.

I have simplified the example without posting the ode simulation code.

I have added the code along with the plots at this site: Link

Can anyone explain this seemingly strange behavior?

Any help is greatly appreciated!

Here is example code, that shows what I mean:

library('tidyr')
library('tibble')
library('ggplot2')
library('dplyr')

grid_values <- 2^(-3:3)

strange_values <- c(-1.90819287770871e-06, -1.68820727726686e-20, 1.90820561104585e-06, 
                    -2.03934646947346e-11, -2.66724989539021e-44, 1.82186185543446e-11, 
                    -3.08642000845794e-14, -2.84079624478981e-68, 3.8017746773927e-20, 
                    -1.55431223447522e-14, -2.12106623568441e-87, -7.04031177308046e-34, 
                    1.99840144432528e-15, 6.92960775272386e-94, -2.17911262386235e-50, 
                    6.43929354282591e-15, 1.60655203590779e-101, -2.4149683145618e-74, 
                    4.2188474935756e-15, -1.63364987668272e-101, -8.43744249369279e-100, 
                    -1.9234795292089e-06, -1.40915667489693e-20, 1.92348291032148e-06, 
                    -7.86031240096463e-11, 5.94869638827445e-40, 1.70218514362265e-11, 
                    -6.21724893790088e-15, -5.32110095875999e-63, 3.9895815730536e-20, 
                    2.39808173319034e-14, -9.91626723546227e-86, -2.47375723122866e-33, 
                    -1.77635683940025e-15, 8.7576689576463e-93, -2.1712899716615e-50, 
                    9.54791801177635e-15, 2.7961387551394e-101, -2.62250706570328e-74, 
                    -6.43929354282591e-15, -5.36337882495689e-101, -1.65540646490924e-99, 
                    -1.95935441282824e-06, -4.13414429145914e-22, 1.9595249500527e-06, 
                    -1.99651406518342e-11, 4.01993294485079e-37, 1.71444629227149e-11, 
                    2.31215047108435e-12, -5.46064224913782e-66, 6.44847728373308e-20, 
                    5.40456568387526e-13, 5.30352631285166e-83, 3.81832474229875e-33, 
                    -1.80966353013901e-14, -9.72418279929888e-94, -2.08007912888974e-51, 
                    -1.33226762955019e-14, 3.23934484578975e-100, -2.61033780134937e-74, 
                    6.88338275267597e-15, -1.29762567303952e-99, -2.07383582042798e-98, 
                    -2.01803061317118e-06, 3.3691909504469e-20, 2.01799435665222e-06, 
                    -1.83731918568242e-11, 7.21526941571507e-42, 1.72812031885596e-11, 
                    1.40298883621881e-11, 2.61529894687986e-38, 2.597261897857e-20, 
                    3.95239396766556e-14, -1.83777217239233e-53, 1.74710015191643e-33, 
                    -2.1316282072803e-14, 3.26611237858842e-68, -1.19804995812909e-51, 
                    -1.58761892521397e-14, 6.58410560104933e-90, -2.50682775406401e-74, 
                    2.46469511466785e-14, -1.08556164510476e-96, -8.68448004693709e-96, 
                    -2.14979959756167e-06, 4.65632478870001e-17, 2.14994451996064e-06, 
                    -2.15127915481617e-11, -5.03897310277035e-29, 2.37451670641299e-11, 
                    -7.30294713591206e-11, -6.74709311307118e-38, 4.03149402823541e-20, 
                    8.21565038222616e-14, 4.6575341905728e-50, -1.71156811032874e-33, 
                    -1.32116539930394e-14, 9.41355218246985e-67, -5.35957793195957e-51, 
                    7.99360577730113e-15, 8.43929875779189e-89, -2.9418326640071e-74, 
                    1.48769885299771e-14, -2.81028796325013e-90, -1.12411483527064e-89, 
                    -2.42728809329851e-06, -8.05503632048299e-18, 2.42718074969143e-06, 
                    5.7643223527748e-11, -5.67417009881705e-30, 2.18227445666839e-11, 
                    4.88498130835069e-15, 5.74369923731793e-37, 5.93253926283155e-20, 
                    -5.36681810103801e-13, 7.68115012003888e-48, 2.12048592220925e-31, 
                    1.43107747874183e-12, -5.9458568180203e-64, 3.32402936140172e-48, 
                    -8.88178419700125e-16, -1.75086766216852e-75, -3.32876019974183e-73, 
                    6.43929354282591e-15, -1.00992378651113e-74, -2.01984753722959e-74, 
                    -2.90572647954068e-06, -7.77642264438329e-10, 2.90649964611508e-06, 
                    9.09130548620851e-11, -3.52178085798882e-12, -8.73905452509179e-11, 
                    -1.03369389016228e-05, 6.07960561736676e-07, 9.72897833978829e-06, 
                    -0.00081769791399311, 9.032308610189e-05, 0.000727374827890998, 
                    -0.0011992740379827, 0.000238928931343064, 0.000960345106639307, 
                    -0.00123663646030969, 0.000411530217922524, 0.000825106242386583, 
                    -0.00124466009860591, 0.000621942028670438, 0.000622718069935415
)
my_tib <- expand_grid(beta = grid_values, lambda = grid_values, name = c('S', 'I', 'R'))
my_tib$value <- 0
my_tib$value[my_tib$name == 'I'] <- 1
my_tib$value_strange <- my_tib$value   strange_values


# expected behavior:
my_tib %>%
  ggplot(aes(x = beta, y = value, fill = name))   geom_area()   facet_grid(cols = vars(lambda))   scale_x_continuous(trans = 'log10')

# strange behavior when adding these really small, strange (?) numbers:
my_tib %>%
  ggplot(aes(x = beta, y = value_strange, fill = name))   geom_area()   facet_grid(cols = vars(lambda))   scale_x_continuous(trans = 'log10')

# expected behavior when x axis is not on log-scale
my_tib %>%
  ggplot(aes(x = beta, y = value_strange, fill = name))   geom_area()   facet_grid(cols = vars(lambda))

# expected behavior when only the 1's are plotted and the 0's are omitted
my_tib %>% filter(name == 'I') %>%
  ggplot(aes(x = beta, y = value_strange, fill = name))   geom_area()   facet_grid(cols = vars(lambda))   scale_x_continuous(trans = 'log10')

# can't reproduce strange behavior with random numbers - what makes the other numbers so strange that `geom_area` produces weird results?
set.seed(1)
my_tib$value_strange_2 <- my_tib$value   runif(nrow(my_tib), -1e-10, 1e-10)
my_tib %>%
  ggplot(aes(x = beta, y = value_strange_2, fill = name))   geom_area()   facet_grid(cols = vars(lambda))   scale_x_continuous(trans = 'log10')

sessionInfo()

Does anyone have an idea why that is?

CodePudding user response：

Actually, I am somewhat surprised that your code works at all. I believe this is (as often when weird polygons are being drawn) rather a grouping issue. You will need to tell ggplot2 that you are dealing with an interaction of your variables, in your case lambda and beta.

Very unsure why your specific problem happens only sometimes and in this particular instance, though. It remains weird.

library(tidyverse)

my_tib %>%
  ggplot(aes(x = beta, y = value_strange, fill = name,
   group = interaction(lambda, name)))   
  geom_area()   
  facet_grid(cols = vars(lambda))   
  scale_x_continuous(trans = 'log10')

^{Created on 2023-02-02 with reprex v2.0.2}

CodePudding user response：

Thanks for the input!

At least I know how to circumvent the problem now. I still have an impression this might be undesired behavior and I will file an issue at the github repository of the ggplot2 package!

Best greetings, Sebastian