Detecting Vehicle locations using R

I have a data frame of vehicle trajectories. Here's a snapshot:

dput(head(df))structure(list(vehicle = c(2L, 2L, 2L, 2L, 2L, 2L),

frame = 43:48,     globalx = c(6451214.156, 6451216.824, 6451219.616,
6451222.548,     6451225.462, 6451228.376), class = c(2L, 2L, 2L, 2L,
2L,     2L), velocity = c(37.76, 37.9, 38.05, 38.18, 38.32, 38.44    ),
lane = c(2L, 2L, 2L, 2L, 2L, 2L)), .Names = c("vehicle", "frame",
"globalx", "class", "velocity", "lane"), row.names = c(NA, 6L), class =
"data.frame")
where, vehicle= vehicle id, frame= frame id of time frames in which it
was observed, globalx = x coordinate of the front center of the
vehicle, class=type of vehicle (1=motorcycle, 2=car, 3=truck),
velocity=speed of vehicles in feet per second, lane= lane number (there
are 6 lanes).The 'frame' represents one tenth of a second i.e. one
frame is 0.1 seconds long. At frame 't' the vehicle has globalx
coordinate x(t) and at frame 't-1' (0.1 seconds before) it was x(t-1).
If the reference location has globalx coordinate=6451179.1116 then I
simply want a new column in df called 'u' which has 'yes' in the row
where globalx of the vehicle was greater than reference coordinate at
'U' AND the previous consecutive globalx coordinate of this vehicle was
less than reference coordinate at 'U'(i.e. reference coordinate is
between the 2 locations of vehicle in two consecutive frames). This
means that if df has 100 vehicles then there will be 100 'yes' in 'u'
column because every vehicle wil!


l meet the above criteria only once. I have tried to do this by running
the function with ifelse and also tried to do the same using a for loop
but it doesn't work for me.


		 	   		  
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