R help - Jan 2010 - plotting moving range control chart

I have been having the same problem as poster Hodgess, below. It appears
that her question was never answered, so I would like to share a solution
with the community.

The problem is the (apparent?) inability to produce moving range process
behavior (a.k.a. "control") charts with individuals data in the
package
"qcc" (v. 2.0). I have also struggled with the same limitation in
package
"IQCC" (v. 1.0).

The package "qAnalyst" (v. 0.6.0) provides an option to produce a
moving
range chart with individuals data. The example given in the qAnalyst manual
for function spc yields an individuals chart:
> #i-chart, moving range to estimate st. dev. is equal to 2 points with
testType=1,
> data(rawWeight)
> ichart=spc(x=rawWeight$rawWeight, sg=2, type="i",
name="weight",
testType=1)
> plot(ichart)
> summary(ichart)
Changing "type = 'i'" to "type = 'mr'"
yields the moving chart:
> mrchart = spc(x = rawWeight$rawWeight, sg = 2, type = "mr", name
"weight", testType = 1)
> plot(mrchart)
> summary(mrchart)
In separate tests, I have confirmed that qAnalyst correctly computes natural
process limits (a.k.a. "control limits") for X-bar and R charts, using
the
average of the subgroup means. I have not yet checked the calculations for
the ImR or other charts.

An additional difference between these packages is that qAnalyst uses the
lattice library to generate output, while the other two packages appear to
use the (traditional) graphics library.

Regards,

Tom


On Tue, 10 Nov 2009 23:39:23 -0600, Erin Hodgess
<erinm.hodgess_at_gmail.com<erinm.hodgess_at_gmail.com?Subject=Re:%20[R]%20%20plotting%20moving%20range%20control%20chart>>
wrote:
> Dear R People:
>
> I am using qcc for a quality control class.
>
> I have used qcc with type "xbar.one" for individuals but cannot
determine
> how to plot a moving range control chart.
>
> Has anyone done that, please?
>
> Thanks,
> Erin
>
> --
> Erin Hodgess
> Associate Professor
> Department of Computer and Mathematical Sciences
> University of Houston - Downtown
> mailto: erinm.hodgess_at_gmail.com
>
>
	[[alternative HTML version deleted]]

Tom Hopper wrote:
>The problem is the (apparent?) inability to produce moving range process
>behavior (a.k.a. "control") charts with individuals data in the
package
>"qcc" (v. 2.0). I have also struggled with the same limitation in
package
>"IQCC" (v. 1.0).
    The
moving range chart has the same control limit factors (viz., D3, D4) as the
range chart, so
one should be able to feed an appropriately-constructed matrix into
qcc(type = "R").  In other words, if one can transform the original
individual observations 1..m into 1..(m - 1) rational subgroups of
size two so that the range of the rational
subgroup i equals the moving range of the individual observations i and
i+1, it'll fool qcc's range chart into plotting the moving ranges (MR)
as the range (R), computing the center line as the average MR instead
of the average R, and computing the control limits as D3*MR and D4*MR
instead of D3*R and D4*R.

    My solution for qcc, using Montgomery's viscosity data in
"viscosity.txt":

batch viscosity phase
   1      34.05 setup
   2      34.40 setup
   3      33.59 setup
   ...


observations <- read.table("viscosity.txt", TRUE)

require(qcc)
attach(observations)

# identify "observation" and "batch" columns as providing
the
# observations and unit numbers
observation <- qcc.groups(viscosity, batch)

# number of batches in phase I ("setup")
m <- length(phase[phase == "setup"])

# extract the batch numbers to display for the phase II ("monitoring")
data
setupBatches <- as.character(batch[phase == "setup"])
monitoringBatches <- as.character(batch[phase == "monitoring"])

# plot xbar chart
obj <- qcc(data = observation[1,1:m],
           type = "xbar.one",
           newdata = observation[1,-(1:m)],
            labels = setupBatches,
            newlabels = monitoringBatches,
           axes.las = 3,
           chart.all = TRUE,
           title = "Individuals chart for aircraft primer paint
viscosity",
           xlab = "Batch",
           ylab = "Value (viscosity units)")

setupBatches <- setupBatches[-1]
numberOfBatches <- length(observation)

# intermediate matrix to coax qcc into plotting a moving range chart
#
#    observations x[i], x[i + 1] appear in adjacentObservations[i]
#    whose range equals the moving range |x[[i]] - x[[i + 1]]|
#
adjacentObservations <- matrix(nrow = length(observation) - 1, ncol = 2)
adjacentObservations[,1] <- observation[1,1:numberOfBatches - 1];
adjacentObservations[,2] <- observation[1,2:numberOfBatches];

# plot MR chart
obj <- qcc(data = adjacentObservations[1:m - 1,],
           type = "R",
           newdata = adjacentObservations[-(1:m - 1),],
           labels = setupBatches,
           newlabels = monitoringBatches,
           axes.las = 3,
           chart.all = TRUE,
           title = "MR chart for aircraft primer paint viscosity",
           xlab = "Batch",
           ylab = "Moving range (viscosity units)")