Frequency polygons are an alternative to histograms that make it simpler to overlay multiple distributions.

```
freqpolygon(
x,
...,
panel = "panel.freqpolygon",
prepanel = "prepanel.default.freqpolygon"
)
prepanel.default.freqpolygon(
x,
darg = list(),
plot.points = FALSE,
ref = FALSE,
groups = NULL,
subscripts = TRUE,
jitter.amount = 0.01 * diff(current.panel.limits()$ylim),
center = NULL,
nint = NULL,
breaks = NULL,
width = darg$width,
type = "density",
...
)
panel.freqpolygon(
x,
darg = list(),
plot.points = FALSE,
ref = FALSE,
groups = NULL,
weights = NULL,
jitter.amount = 0.01 * diff(current.panel.limits()$ylim),
type = "density",
breaks = NULL,
nint = NULL,
center = NULL,
width = darg$width,
gcol = trellis.par.get("reference.line")$col,
glwd = trellis.par.get("reference.line")$lwd,
h,
v,
...,
identifier = "freqpoly"
)
```

- x
a formula or a numeric vector

- ...
additional arguments passed on to

`histogram()`

and`panel`

.- panel
a panel function

- prepanel
a prepanel function

- darg
a list of arguments for the function computing the frequency polygon. This exists primarily for compatibility with

`densityplot`

and is unlikely to be needed by the end user.- plot.points
one of

`TRUE`

,`FALSE`

,`"jitter"`

, or`"rug"`

indicating how points are to be displayed- ref
a logical indicating whether a horizontal reference line should be added (roughly equivalent to

`h=0`

)- groups, weights, jitter.amount, identifier
as in

`densityplot()`

or`histogram()`

- subscripts
as in other lattice prepanel functions

- center
center of one of the bins

- nint
an approximate number of bins for the frequency polygon

- breaks
a vector of breaks for the frequency polygon bins

- width
width of the bins

- type
one of

`'density'`

,`'percent'`

, or`'count'`

- gcol
color of guidelines

- glwd
width of guidelines

- h, v
a vector of values for additional horizontal and vertical lines

a trellis object

This function make use of `histogram`

to determine overall layout. Often
this works reasonably well but sometimes it does not. In particular, when `groups`

is
used to overlay multiple frequency polygons, there is often too little head room.
In the latter cases, it may be
necessary to use `ylim`

to determine an appropriate viewing rectangle for the
plot.

```
freqpolygon(~age | substance, data=HELPrct, v=35)
freqpolygon(~age, data=HELPrct, labels=TRUE, type='count')
freqpolygon(~age | substance, data=HELPrct, groups=sex)
freqpolygon(~age | substance, data=HELPrct, groups=sex, ylim=c(0,0.11))
## comparison of histogram and frequency polygon
histogram(~eruptions, faithful, type='density', width=.5)
ladd( panel.freqpolygon(faithful$eruptions, width=.5 ))
```