Invalid levels for facet_grid in ggplot2

Question

I worked with a variant of this code:

library(ggplot2)

Compare = matrix(c(
0,           0,           "Soil 1", "tF",
0.379268025, 5.555806214, "Soil 1", "tF",
0.961561989, 13.05580621, "Soil 1", "tF",
1.55418685,  20.55580621, "Soil 1", "tF",
0,           0,           "Soil 2", "tF",
0.104297312, 1.581249799, "Soil 2", "tF",
0.705818262, 6.081249799, "Soil 2", "tF",
1.447379092, 10.5812498,  "Soil 2", "tF",
0,           20,          "Soil 1", "tf",
0.379268025, 13.1603086,  "Soil 1", "tf",
0.961561989, 12.72354396, "Soil 1", "tf",
1.55418685,  12.60549558, "Soil 1", "tf",
0,           20,          "Soil 2", "tf",
0.104297312, 10.51383279, "Soil 2", "tf",
0.705818262, 6.433709727, "Soil 2", "tf",
1.447379092, 5.82398083,  "Soil 2", "tf",
0,           0,           "Soil 1", "zf",
0.379268025, 205.7706005, "Soil 1", "zf",
0.961561989, 483.5483783, "Soil 1", "zf",
1.55418685,  761.3261561, "Soil 1", "zf",
0,           0,           "Soil 2", "zf",
0.104297312, 23.25367352, "Soil 2", "zf",
0.705818262, 89.43014411, "Soil 2", "zf",
1.447379092, 155.6066147, "Soil 2", "zf"), nrow = 24, ncol = 4, byrow = TRUE)

plot = ggplot(as.data.frame(Compare),
aes(as.double(Compare[,1]), as.double(Compare[,2]), color = Compare[,3])) +
    geom_point() + facet_grid(Compare[,4] ~ .)
plot

My problem is with the aspect of the facet_grid()code. If I comment on this or delete it, it works fine, so I know that I can isolate my problem to the point that it is related. What I'm trying to accomplish is a set of three panels arranged vertically, with Compare[,1]the x axis, Compare[,2]the y axis, coloring based on Compare[,3](creating a set of points for both soils types on each facet) and three faces, made in accordance with Compare[,4].

The error I get when starting with the facet_grid()included in the code:

Error in layout_base(data, rows, drop = drop) : 
    At least one layer must contain all variables used for facetting

I feel that my error may be related to forcing doubles and dataframes to handle the original form of the matrix, but I'm not sure what needs to be changed.

Answer 1

, facet_grid.

• . , data.frame.
• as.double factor numeric ( , → data.frame.
• ggplot aes , , [.
• facet_grid names, .

, .

CP <- as.data.frame(Compare)

CP[[1]] <- as.numeric(as.character(CP[[1]]))
CP[[2]] <- as.numeric(as.character(CP[[2]]))
# your data.frame names are..
names(CP)
# [1] "V1" "V2" "V3" "V4"

ggplot(CP, aes(x = V1, y = V2, colour = V3)) +
 geom_point() + facet_grid(V4 ~ . )