替换在for循环中的长度为零

Question

当我尝试使用while循环（在末尾）时，它给出的替换长度为零（我也尝试过for循环）。我看到其他与此相关的帖子可以解决此问题，但似乎没有任何工作可做。我正在附上R代码

library(ggplot2)

Data <- readMat("C:\\Users\\syeda\\Desktop\\Reserach PhD\\Data\\gait.mat")

#To separate Knee variable

kne<-Data$knee

knt<-seq(0,1,len=7)
#knt<-knt[2:length(knt)-1]
wbasis <- create.bspline.basis(c(0,1), nbasis=9,norder=4,breaks = knt)
knefdPar <- fdPar(wbasis, 2, 10^(-0.5))
##??##
kneMon <- smooth.monotone(t, rowMeans(kne), knefdPar)
hgtfhatfd <- kneMon$yhatfd
accelfdUN <- deriv.fd(hgtfhatfd, 2)
accelmeanfdUN <- mean(accelfdUN)

PGSctr <- rep(0,39)
agefine <- seq(0,1,len=200)
par(mfrow=c(1,1), ask=TRUE)

for (icase in 1:39) {
  accveci <- predict(accelfdUN[icase], agefine)
  plot(agefine,accveci,"l", ylim=c(-10,80),
       xlab="Year", ylab="Height Accel.",
       main=paste("Case",icase))
  lines(c(0,1),c(0,0),lty=2)
  PGSctr[icase] = locator(icase)$
  print(PGSctr[icase])
}

i<-1
while (i<40) {
  accveci <- predict(accelfdUN[i], agefine)
  plot(agefine,accveci,"l", ylim=c(-10,80),
       xlab="Year", ylab="Height Accel.",
       main=paste("Case",i))
  lines(c(0,1),c(0,0),lty=2)
  PGSctr[i] <- locator(1)$x
  #print(locator(i)$x)
  i<-i+1
}