Error in if (!n.cat[i]) { : argument is of length zero - r

Question

I just begin to learn to code using R and I tried to do a classification by C5.0. But I encounter some problems and I don't understand. I am looking for help with gratitude. Below is the code I learned from someone and I tried to use it to run my own data:
require(C50)
data.resultc50 <- c()
prematrixc50 <- c()
for(i in 3863:3993)
{
needdata$class <- as.factor(needdata$class)
trainc50 <- C5.0(class ~ ., needdata[1:3612,], trials=5, control=C5.0Control(noGlobalPruning = TRUE, CF = 0.25))
predc50 <- predict(trainc50, newdata=testdata[i, -1], trials=5, type="class")
data.resultc50[i-3862] <- sum(predc50==testdata$class[i])/length(predc50)
prematrixc50[i-3862] <- as.character.factor(predc50)
}
Belows are two objects needdata & testdata I used in the code above with part of their heads respectively:
class Volume MA20 MA10 MA120 MA40 MA340 MA24 BIAS10
1 1 2800 8032.00 8190.9 7801.867 7902.325 7367.976 1751 7.96
2 1 2854 8071.40 8290.3 7812.225 7936.550 7373.624 1766 6.27
3 0 2501 8117.45 8389.3 7824.350 7973.250 7379.444 1811 5.49
4 1 2409 8165.40 8488.1 7835.600 8007.900 7385.294 1825 4.02
# the above is "needdata" and actually has 15 variables with 3862 obs.
class Volume MA20 MA10 MA120 MA40 MA340 MA24 BIAS10
1 1 2800 8032.00 8190.9 7801.867 7902.325 7367.976 1751 7.96
2 1 2854 8071.40 8290.3 7812.225 7936.550 7373.624 1766 6.27
3 0 2501 8117.45 8389.3 7824.350 7973.250 7379.444 1811 5.49
4 1 2409 8165.40 8488.1 7835.600 8007.900 7385.294 1825 4.02
# the above is "testdata" and has 15 variables with 4112 obs.
The data above contain the factor class with value of 0 & 1. After I run it I got warnings below:
In predict.C5.0(trainc50, newdata = testdata[i, -1], trials = 5, ... : 'trials' should be <= 1 for this object. Predictions generated
using 1 trials
And when I try to look at the object trainc50 just created, I noticed the number of boosting iterations is 1 due to early stopping as shown below:
# trainc50
Call:
C5.0.formula(formula = class ~ ., data = needdata[1:3612, ],
trials = 5, control = C5.0Control(noGlobalPruning = TRUE,
CF = 0.25), earlyStopping = FALSE)
Classification Tree
Number of samples: 3612
Number of predictors: 15
Number of boosting iterations: 5 requested; 1 used due to early stopping
Non-standard options: attempt to group attributes, no global pruning
I also tried to plot the decision tree and I got the error as below:
plot(trainc50)
Error in if (!n.cat[i]) { : argument is of length zero
In addition: Warning message:
In 1:which(out == "Decision tree:") : numerical expression has 2 elements: only the first used
Does that mean my code is too bad to perform further trials while running C5.0? What is wrong? Can someone please help me out about why do I encounter early stopping and what does the error and waring message mean? How can I fix it? If anyone can help me I'll be very thankful.

Answer 1

Used in
http://r-project-thanos.blogspot.tw/2014/09/plot-c50-decision-trees-in-r.html
using function
C5.0.graphviz(firandomf,
"a.txt",
fontname='Arial',
col.draw='black',
col.font='blue',
col.conclusion='lightpink',
col.question='grey78',
shape.conclusion='box3d',
shape.question='diamond',
bool.substitute=c('None', 'yesno', 'truefalse', 'TF'),
prefix=FALSE,
vertical=TRUE)
And in the command line:
pip install graphviz
dot -Tpng ~plot/a.txt >~/plot/a.png