How to continuously send data from LabVIEW to R? (code help) - r

Question

I am trying to bring real time data from LabVIEW (vibration of a bearing and temperature) into an app written in R to create a control chart. It works for a while but eventually crashes with the following error message:
Error in aggregate.data.frame(B, list(rep(1:(nrow(B)%/%n + 1), each = n, :
no rows to aggregate
The process works as LabVIEW takes the data and projects it onto two Excel files. Those files are read in the R code and used to project a control chart in R. The process succeeds for some time, and the failure moment is not always the same amount of time. Sometimes the control chart will run for 6-7 min, other times is will crash in 2 min.
My suspicion is that the Excel files are not being updated fast enough, so the R code tries to read that Excel file when it is empty.
Any suggestions would be great! thank you!
I have tried to lower the sample size taken per second. That did not work.
getwd()
setwd("C:/Users/johnd/Desktop/R Data")
while(1) {
A = fread("C:/Users/johnd/Desktop/R Data/a1.csv" , skip = 4 , header = FALSE , col.names = c("t1","B2","t2","AM","t3","M","t4","B1"))
t1 = A$t1
B2 = A$B2
t2 = A$t2
AM = A$AM
t3 = A$t3
M = A$M
t4 = A$t4
B1 = A$B1
B = fread("C:/Users/johnd/Desktop/R Data/b1.csv" , skip = 4 , header = FALSE , col.names = c("T1","small","T2","big"))
T1 = B$T1
small = B$small
T2 = B$T2
big = B$big
DJ1 = A[seq(1,nrow(A),1),c('t1','B2','AM','M','B1')]
DJ1
n = 16
DJ2 = aggregate(B,list(rep(1:(nrow(B)%/%n+1),each=n,len=nrow(B))),mean)[-1]
DJ2
#------------------------------------------------------------------------
DJ6 = cbind(DJ1[,'B1'],DJ2[,c('small','big')]) # creates matrix for these three indicators
DJ6
#--------------T2 Hand made---------------------------------------------------------------------
new_B1 = DJ6[,'B1']
new_small = DJ6[,'small'] ### decompose the DJ6 matrix into vectors for each indicator(temperature, big & small accelerometers)
new_big = DJ6[,'big']
new_B1
new_small
new_big
mean_B1 = as.numeric(colMeans(DJ6[,'B1']))
mean_small = as.numeric(colMeans(DJ6[,'small'])) ##decomposes into vectors of type numeric
mean_big = as.numeric(colMeans(DJ6[,'big']))
cov_inv = data.matrix(solve(cov(DJ6))) # obtain inverse covariance matrix
cov_inv
p = ncol(DJ6) #changed to pull number of parameters by taking the number of coumns in OG matrix #p=3 # #ofQuality Characteristics
m=64 # #of samples (10 seconds of data)
a_alpha = 0.99
f= qf(a_alpha , df1 = p,df2 = (m-p)) ### calculates the F-Statistic for our data
f
UCL = (p*(m+1)*(m-1)*(f))/(m*(m-p)) ###produces upper control limit
UCL
diff_B1 = new_B1-mean_B1
diff_small = new_small-mean_small
diff_big = new_big-mean_big
DJ7 = cbind(diff_B1, diff_small , diff_big) #produces matrix of difference between average and observations (x-(x-bar))
DJ7
# DJ8 = data.matrix(DJ7[1,])
# DJ8
DJ9 = data.matrix(DJ7) ### turns matrix into appropriate numeric form
DJ9
# T2.1.1 = DJ8 %*% cov_inv %*% t(DJ8)
# T2.1.1
# T2.1 = t(as.matrix(DJ9[1,])) %*% cov_inv %*% as.matrix(DJ9[1,])
# T2.1
#T2 <- NULL
for(i in 1:64){ #### creates vector of T^2 statistic
T2<- t(as.matrix(DJ9[i,])) %*% cov_inv %*% as.matrix(DJ9[i,]) # calculation of T^2 test statistic ## there is no calculation of x-double bar
write.table(T2,"C:/Users/johnd/Desktop/R Data/c1.csv",append=T,sep="," , col.names = FALSE)#
#
DJ12 <-fread("C:/Users/johnd/Desktop/R Data/c1.csv" , header = FALSE ) #
}
# DJ12
DJ12$V1 = 1:nrow(DJ12)
# plot(DJ12 , type='l')
p1 = nrow(DJ12)-m
p2 = nrow(DJ12)
plot(DJ12[p1:p2,], type ='o', ylim =c(0,15), ylab="T2 Chart" , xlab="Data points") ### plots last 640 points
# plot(DJ12[p1:p2,], type ='o' , ylim =c(0,15) , ylab="T2 Chart" , xlab="Data points")
abline(h=UCL , col="red") ## displays upper control limit
Sys.sleep(1)
}

Answer 1

The process succeeds for some time, and the failure moment is not always the same amount of time. Sometimes the control chart will run for 6-7 min, other times is will crash in 2 min.
My suspicion is that the Excel files are not being updated fast enough, so the R code tries to read that Excel file when it is empty.
Your suspicion is correct.
With your current design, your R application can crash depending on how fast it runs relative to your LabVIEW application. This is called a race condition; you must eliminate race conditions from your code.
A quick and dirty solution
One simple solution to avoid the crash is to call NROW to check if any data exists. If there's no data available, don't call aggregate. This is described here: error message in r: no rows to aggregate
A more robust solution
A better solution is to use a communications protocol like TCP to stream data from LabVIEW to R, instead of using CSV files to transfer real-time data. For example, your R program could listen for data on a TCP socket. Make it wait for data to be sent from LabVIEW before running your data processing code.
Here is an example on using socketConnection in R: http://blog.corynissen.com/2013/05/using-r-to-communicate-via-socket.html
Here is an example on sending/receiving data over TCP in LabVIEW: http://www.ni.com/product-documentation/2710/en/