# R: Histograms and Kernel Density Plots

histogram {lattice} | R Documentation

## Histograms and Kernel Density Plots

### Description

Draw Histograms and Kernel Density Plots, possibly conditioned on other variables.

### Usage

    histogram(x, data, ...)
    densityplot(x, data, ...)
    ## S3 method for class 'formula':
    histogram(x,
              data,
              allow.multiple, outer = TRUE,
              auto.key = FALSE,
              aspect = "fill",
              panel = lattice.getOption("panel.histogram"),
              prepanel, scales, strip, groups,
              xlab, xlim, ylab, ylim,
              type = c("percent", "count", "density"),
              nint = if (is.factor(x)) nlevels(x)
              else round(log2(length(x)) + 1),
              endpoints = extend.limits(range(x, finite = TRUE), prop = 0.04),
              breaks,
              equal.widths = TRUE,
              drop.unused.levels = lattice.getOption("drop.unused.levels"),
              ...,
              lattice.options = NULL,
              default.scales = list(),
              subscripts,
              subset)

    ## S3 method for class 'numeric':
    histogram(x, data = NULL, xlab, ...)
    ## S3 method for class 'factor':
    histogram(x, data = NULL, xlab, ...)

    ## S3 method for class 'formula':
    densityplot(x,
                data,
                allow.multiple = is.null(groups) || outer,
                outer = !is.null(groups),
                auto.key = FALSE,
                aspect = "fill",
                panel = lattice.getOption("panel.densityplot"),
                prepanel, scales, strip, groups,
                xlab, xlim, ylab, ylim,
                bw, adjust, kernel, window, width, give.Rkern,
                n = 50, from, to, cut, na.rm,
                drop.unused.levels = lattice.getOption("drop.unused.levels"),
                ...,
                lattice.options = NULL,
                default.scales = list(),
                subscripts,
                subset)
    ## S3 method for class 'numeric':
    densityplot(x, data = NULL, xlab, ...)

    do.breaks(endpoints, nint)

### Arguments

`x`

The object on which method dispatch is carried out.
For the `formula` method, a formula of the form `~ x | g1 * g2 * ...` indicates that histograms or Kernel Density estimates of `x` should be produced conditioned on the levels of the (optional) variables `g1, g2, ...`. `x` can be numeric (or factor for `histogram`), and each of `g1, g2, ...` must be either factors or shingles.
As a special case, the right hand side of the formula can contain more than one variable separated by a `+` sign. What happens in this case is described in details in the documentation for `xyplot`. Note that in either form, all the variables involved in the formula have to have same length.
For the `numeric` and `factor` methods, `x` replaces the `x` vector described above. Conditioning is not allowed in these cases.

`data` | For the `formula` method, an optional data frame in which variables are to be evaluated. Ignored with a warning in other cases.
`type` | Character string indicating type of histogram to be drawn. `"percent"` and `"count"` give relative frequency and frequency histograms, and can be misleading when breakpoints are not equally spaced. `"density"` produces a density scale histogram. `type` defaults to `"percent"`, except when the breakpoints are unequally spaced or `breaks = NULL`, when it defaults to `"density"`.
`nint` | Number of bins. Applies only when `breaks` is unspecified or `NULL` in the call. Not applicable when the variable being plotted is a factor.
`endpoints` | vector of length 2 indicating the range of x-values that is to be covered by the histogram. This applies only when `breaks` is unspecified and the variable being plotted is not a factor. In `do.breaks`, this specifies the interval that is to be divided up.

`breaks`

usually a numeric vector of length (number of bins + 1) defining the breakpoints of the bins. Note that when breakpoints are not equally spaced, the only value of `type` that makes sense is density. When unspecified, the default is to use

          breaks = seq_len(1 + nlevels(x)) - 0.5

when `x` is a factor, and

          breaks = do.breaks(endpoints, nint)

otherwise. Breakpoints calculated in such a manner are used in all panels.
Other values of `breaks` are possible, in which case they affect the display in each panel differently. A special value of `breaks` is `NULL`, in which case the number of bins is determined by `nint` and then breakpoints are chosen according to the value of `equal.widths`. Other valid values of `breaks` are those of the `breaks` argument in `hist`. This allows specification of `breaks` as an integer giving the number of bins (similar to `nint`), as a character string denoting a method, and as a function.

`equal.widths` | logical, relevant only when `breaks=NULL`. If `TRUE`, equally spaced bins will be selected, otherwise, approximately equal area bins will be selected (this would mean that the breakpoints will not be equally spaced).
`n` | number of points at which density is to be evaluated
`panel` | The function that uses the packet (subset of display variables) corresponding to a panel to create a display. Default panel functions are documented separately, and often have arguments that can be used to customize its display in various ways. Such arguments can usually be directly supplied to the high level function.
`allow.multiple, outer, auto.key, aspect, prepanel, scales, strip, groups, xlab, xlim, ylab, ylim, drop.unused.levels, lattice.options, default.scales, subscripts, subset` | See `xyplot`
`bw, adjust, kernel, window, width, give.Rkern, from, to, cut, na.rm` | arguments to `density`, passed on as appropriate
`...` | Further arguments. See corresponding entry in `xyplot` for non-trivial details.

### Details

`histogram` draws Conditional Histograms, while `densityplot` draws Conditional Kernel Density Plots. The density estimate in `densityplot` is actually calculated using the function `density`, and all arguments accepted by it can be passed (as `...`) in the call to `densityplot` to control the output. See documentation of `density` for details. (Note: The default value of the argument `n` of `density` is changed to 50.)

These and all other high level Trellis functions have several arguments in common. These are extensively documented only in the help page for `xyplot`, which should be consulted to learn more detailed usage.

`do.breaks` is an utility function that calculates breakpoints given an interval and the number of pieces to break it into.

### Value

An object of class `"trellis"`. The `update` method can be used to update components of the object and the `print` method (usually called by default) will plot it on an appropriate plotting device.

### Note

The form of the arguments accepted by the default panel function `panel.histogram` is different from that in S-PLUS. Whereas S-PLUS calculates the heights inside `histogram` and passes only the breakpoints and the heights to the panel function, here the original variable `x` is passed along with the breakpoints. This allows plots as in the second example below.

### Author(s)

Deepayan Sarkar Deepayan.Sarkar@R-project.org

### See Also

`xyplot`, `panel.histogram`, `density`, `panel.densityplot`, `panel.mathdensity`, `Lattice`

### Examples

    require(stats)
    histogram( ~ height | voice.part, data = singer, nint = 17,
              endpoints = c(59.5, 76.5), layout = c(2,4), aspect = 1,
              xlab = "Height (inches)")

    histogram( ~ height | voice.part, data = singer,
              xlab = "Height (inches)", type = "density",
              panel = function(x, ...) {
                  panel.histogram(x, ...)
                  panel.mathdensity(dmath = dnorm, col = "black",
                                    args = list(mean=mean(x),sd=sd(x)))
              } )

    densityplot( ~ height | voice.part, data = singer, layout = c(2, 4),
                xlab = "Height (inches)", bw = 5)

[Package lattice version 0.16-5 Index]