# n2mfrow: Compute Default 'mfrow' From Number of Plots

 n2mfrow R Documentation

## Compute Default 'mfrow' From Number of Plots

### Description

Easy setup for plotting multiple figures (in a rectangular layout) on one page. This computes a sensible default for `par(mfrow)`.

### Usage

```n2mfrow(nr.plots, asp = 1)
```

### Arguments

 `nr.plots` integer; the number of plot figures you'll want to draw. `asp` positive number; the target aspect ratio (columns / rows) in the output. Was implicitly hardwired to `1`; because of that and back compatibility, there is a somewhat discontinuous behavior when varying `asp` around 1, for `nr.plots <= 12`.

### Value

A length-two integer vector `(nr, nc)` giving the positive number of rows and columns, fulfilling `nr * nc >= nr.plots`, and currently, for `asp = 1`, `nr >= nc >= 1`.

### Note

Conceptually, this is a quadratic integer optimization problem, with inequality constraints nr >= 1, nc >= 1, and nr.plots >= nr*nc (and possibly `nr >= asp*nc`), and two objective functions which would have to be combined via a tuning weight, say w, to, e.g., (nr.plots - nr*nc) + w |nr/nc - asp|.

The current algorithm is simple and not trying to solve one of these optimization problems.

### Author(s)

Martin Maechler; suggestion of `asp` by Michael Chirico.

`par`, `layout`.

### Examples

```require(graphics)

n2mfrow(8) # 3 x 3

n <- 5 ; x <- seq(-2, 2, length.out = 51)
## suppose now that 'n' is not known {inside function}
op <- par(mfrow = n2mfrow(n))
for (j in 1:n)
plot(x, x^j, main = substitute(x^ exp, list(exp = j)), type = "l",
col = "blue")

sapply(1:14, n2mfrow)
sapply(1:14, n2mfrow, asp=16/9)
```