Die Ästhetik muss entweder die Länge eins oder dieselbe Länge wie die dataProblems haben

Ich möchte ein Diagramm mit X-Werten als Teilmenge der Messung und Y-Werten als weiterer Teilmenge der gemessenen Daten erstellen.

Im folgenden Beispiel habe ich 4 Produkte p1, p2, p3 und p4. Die Preise richten sich nach Neigung, Farbe und Ausführung. Ich möchte ein facettenreiches Diagramm erstellen, in dem die P3-Produkte (Y-Achse) und die P1-Produkte (X-Achse) dargestellt sind.

Mein Versuch wie folgt ist mit folgendem Fehler kläglich gescheitert:

Fehler: Die Ästhetik muss entweder die Länge eins oder dieselbe Länge wie die dataProblems haben: Teilmenge (Preis, Produkt == "p1"), Teilmenge (Preis, Produkt == "p3")

library(ggplot2)
product=c("p1","p1","p1","p1","p1","p1","p1","p1","p2","p2","p2","p2","p2","p2","p2","p2","p3","p3","p3","p3","p3","p3","p3","p3","p4","p4","p4","p4","p4","p4","p4","p4")
skew=c("b","b","b","b","a","a","a","a","b","b","b","b","a","a","a","a","b","b","b","b","a","a","a","a","b","b","b","b","a","a","a","a")
version=c(0.1,0.1,0.2,0.2,0.1,0.1,0.2,0.2,0.1,0.1,0.2,0.2,0.1,0.1,0.2,0.2,0.1,0.1,0.2,0.2,0.1,0.1,0.2,0.2,0.1,0.1,0.2,0.2,0.1,0.1,0.2,0.2)
color=c("C1","C2","C1","C2","C1","C2","C1","C2","C1","C2","C1","C2","C1","C2","C1","C2","C1","C2","C1","C2","C1","C2","C1","C2","C1","C2","C1","C2","C1","C2","C1","C2")
price=c(1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32)
df = data.frame(product, skew, version, color, price)
# First plot all the data
p1 <- ggplot(df, aes(x=price, y=price, colour=factor(skew))) + geom_point(size=2, shape=19)
p1 <- p1 + facet_grid(version ~ color)
p1 # This gavea very good plot. So far so good
# Now plot P3 vs P1
p1 <- ggplot(df, aes(x=subset(price, product=='p1'), y=subset(price, product=='p3'), colour=factor(skew))) + geom_point(size=2, shape=19)
p1
# failed with: Error: Aesthetics must either be length one, or the same length as the dataProblems:subset(price, product == "p1"), subset(price, product == "p3")

Dies ist das Ergebnis, das ich erwarte: