#
#    Example data-browsing session Tues, 7 Jul 2009
#
#
dat <- read.table( "T08030205.txt", skip=1 ) # must skip header line because
                                             # "Time" not fully labeled

summary(dat)                                # look at column names and 
                                            # data ranges of each column

y <- dat$V7                                 # V7 is to column Ch1a

plot( y )                                   # plot Y vs 1,2,3,.... on X-axis

plot( y, type="l" )                         # lines vs points

plot( y, type="l", xlim=c( 5000, 10000 ) )  # zoom in

plot( y, type="l", xlim=c( 6000, 7000 ) )   # zoom in some more

yp <- y - min(y)                            # move baseline upwards, save in yp

plot( yp, type="l", xlim=c(6000,7000) )     # replot

n <- length( yp )

sig <- ( yp[1:(n-2)] + yp[2:(n-1)] + yp[3:n] ) / 3  # smooth by averaging each
                                                    # point with neighbors
plot( sig, type="l", xlim=c(6000,7000) )             
plot( sig, type="l", xlim=c(6000,6400) )             

# try a peak threshold of 20

sig > 20                                     # boolean vector of positions
                                             # that exceed the threshold

(1:n)[sig > 20]                              # actual positions which exceed

rug( (1:n)[sig > 20] )                       # mark positions with rug

# alternative:

points( sig * (sig > 20), type="l", col="red" ) # overlay masked signal in red