lattice::xyplot/ggplot2: plotting weighted data frames with lmline and smooth

Thanks very much, Dennis. ?See below for something I don't understand.

On 10/21/2011 12:15 PM, Dennis Murphy wrote:

Hi Michael:

Here's one way to get it from ggplot2. To avoid possible overplotting,
I jittered the points horizontally by ? 0.2. I also reduced the point
size from the default 2 and increased the line thickness to 1.5 for
both fitted curves. In ggplot2, the term faceting is synonymous with
conditioning (by groups).

library('HistData')
library('ggplot2')
ggplot(PearsonLee, aes(x = parent, y = child)) +
? ?geom_point(size = 1.5, position = position_jitter(width = 0.2)) +
? ?geom_smooth(method = lm, aes(weights = PearsonLee$weight),
? ? ? ? ? ? ? ?colour = 'green', se = FALSE, size = 1.5) +
? ?geom_smooth(aes(weights = PearsonLee$weight),
? ? ? ? ? ? ? ?colour = 'red', se = FALSE, size = 1.5) +
? ?facet_grid(chl ~ par)

This seems to work, but I don't understand *why*, since the weight variable
is
PearsonLee$frequency, not PearsonLee$weight.

PearsonLee$weight

NULL

I get an error if I try to use PearsonLee$frequency as the weights=
variable.

ggplot(PearsonLee, aes(x = parent, y = child)) +

+ ? ?geom_point(size = 1.5, position = position_jitter(width = 0.2)) +
+ ? ?geom_smooth(method = lm, aes(weights = PearsonLee$frequency),
+ ? ? ? ? ? ? ? ?colour = 'green', se = FALSE, size = 1.5) +
+ ? ?geom_smooth(aes(weights = PearsonLee$frequency),
+ ? ? ? ? ? ? ? ?colour = 'red', se = FALSE, size = 1.5) +
+ ? ?facet_grid(chl ~ par)
Error in eval(expr, envir, enclos) : object 'weight' not found

In the form below, it makes sense to me and does work, using
weight=frequency in the initial aes(),
and weight= in geom_smooth:

ggplot(PearsonLee, aes(x = parent, y = child, weight=frequency)) +
? geom_point(size = 1.5, position = position_jitter(width = 0.2)) +
? geom_smooth(method = lm, aes(weight = PearsonLee$frequency),
? ? ? ? ? ? ? colour = 'green', se = FALSE, size = 1.5) +
? geom_smooth(aes(weight = PearsonLee$frequency),
? ? ? ? ? ? ? colour = 'red', se = FALSE, size = 1.5) +
? facet_grid(chl ~ par)

# If you prefer a legend, here's one take, pulling the legend inside
# to the upper left corner. This requires a bit more 'trickery', but
# the tricks are found in the ggplot2 book.

ggplot(PearsonLee, aes(x = parent, y = child)) +
? ?geom_point(size = 1.5, position = position_jitter(width = 0.2)) +
? ?geom_smooth(method = lm, aes(weights = PearsonLee$weight,
? ? ? ? ? ? ? ?colour = 'Linear'), se = FALSE, size = 1.5) +
? ?geom_smooth(aes(weights = PearsonLee$weight,
? ? ? ? ? ? ? ?colour = 'Loess'), se = FALSE, size = 1.5) +
? ?facet_grid(chl ~ par) +
? ?scale_colour_manual(breaks = c('Linear', 'Loess'),
? ? ? ? ? ? ? ? ? ? ? ?values = c('green', 'red')) +
? ?opts(legend.position = c(0.14, 0.885),
? ? ? ? legend.background = theme_rect(fill = 'white'))


HTH,
Dennis

--
Michael Friendly ? ? Email: friendly AT yorku DOT ca
Professor, Psychology Dept.
York University ? ? ?Voice: 416 736-5115 x66249 Fax: 416 736-5814
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