from ?formula
The models fit by, e.g., the lm and glm functions are specified in a compact symbolic form. The ~ operator is basic in the formation of such models. An expression of the form y ~ model is interpreted as a specification that the response y is modelled by a linear predictor specified symbolically by model. Such a model consists of a series of terms separated by + operators. The terms themselves consist of variable and factor names.
Using formula with variable names fixs it...a fake example follows
library(e1071)
fulldata <- data.frame("label" = gl(2,150),
"V1" = rnorm(300),
"V2" = rnorm(300),
"V3" = rnorm(300),
"V4" = rnorm(300),
"V5" = rnorm(300),
"V6" = rnorm(300),
"V7" = rnorm(300),
"V8" = rnorm(300),
"V9" = rnorm(300),
"V10" = rnorm(300))
str(fulldata)
my.svm <- svm(label ~ .,
probability=TRUE,
na.rm=TRUE,
kernel="linear",
data = fulldata)
my.svm
plot(my.svm,
data = fulldata,
formula = V1 ~ V2)