r - How to put the actual data points on the contour plot with ggplot? -

the code below produces contour plot using ggplot.

xgrid <-  seq(min(mtcars$wt), max(mtcars$wt), 0.3) ygrid <-  seq(min(mtcars$hp), max(mtcars$hp), 0.3)  data.fit <-  expand.grid(wt = xgrid, hp = ygrid)  data.loess <- loess(qsec ~ wt * hp, data = mtcars) mtrx3d <-  predict(data.loess, newdata = data.fit)  mtrx3d[1:4, 1:4]  require(reshape) mtrx.melt <- melt(mtrx3d, id.vars = c("wt", "hp"), measure.vars = "qsec") names(mtrx.melt) <- c("wt", "hp", "qsec")  require(stringr) mtrx.melt$wt <- as.numeric(str_sub(mtrx.melt$wt, str_locate(mtrx.melt$wt, "=")[1,1] + 1)) mtrx.melt$hp <- as.numeric(str_sub(mtrx.melt$hp, str_locate(mtrx.melt$hp, "=")[1,1] + 1))  ggplot(mtrx.melt, aes(x = wt, y = hp, z = qsec)) + stat_contour() 

i wonder how show acutal data points contour lines. have tried

ggplot(mtrx.melt, aes(x = wt, y = hp, z = qsec)) +    stat_contour() + geom_point(mtrx.melt, aes(x = wt, y = hp, z = qsec)) 

but returned error message said

error: ggplot2 doesn't know how deal data of class uneval

this similar question how-can-i-overlay-points-and-lines-onto-a-contour-plot-with-ggplot2 based on different situation. in question, op wants annotate contour plot particular points wants highlight (where these points stored in different data set). case highlight original data points in mtrx.melt. tried method in question failed work.

the plot above not based on dataset, expect have, want have contour plot original data points.

there several issues prevent produce desired result. of mentioned in comments.

however, op wants show actual data points trying plot regular grid mtrx.melt used interpolate data, instead.

the follwing code

library(ggplot2) ggplot(mtrx.melt, aes(x = wt, y = hp, z = qsec))+    geom_point(aes(colour = qsec), mtcars) +   stat_contour(aes(colour = ..level..)) 

creates

which op looking for.

please, note

• the contour levels color coded now.
• the actual data points mtcars data set shown.
• the order of parameters in calls geom_point() , different ggplot. geoms , stats expect aesthetic mapping first parameter , data second.
• geom_point() called before stat_contour() ensure legend title qsec instead of level. beware when replacing stat_contour() geom_tile(). tiles have plotted first layer , points on top.

edit in response this comment op, code have been written

ggplot(mapping = aes(x = wt, y = hp, z = qsec)) +    geom_point(aes(colour = qsec), mtcars) +   geom_contour(aes(colour = ..level..), mtrx.melt) 

this makes more explicit 2 layers, i.e., geom_point() , geom_contour(), being used display data of 2 different data sources. aesthetics shared between both layers placed in initial ggplot() call (which possible here because mtcars , mtrx.melt use same column names). colour aesthetic different, each layer uses own definition.

in call ggplot(), it's required specify parameter name mapping = aes(...) because ggplot() expects data first parameter if unnamed.

geom_contour() used here code appears more consistent , seems preferred on stat_contour() following examples on ggplot2 documentation site.