brk2midp {lazy.tools} R Documentation

## Define Midpoints from Break Points

### Description

Define Midpoints from Break Points

### Usage

```brk2midp(brk, min = NULL)
```

### Arguments

 `brk` a vector of break points. `min` The value of the lowest midpoint. This has priority over margin.

### Details

Break values from midpoint values:
`brk[1]=midp[1] - margin`
`brk[2]=midp[1] + (midp[2]-midp[1])/2`
`brk[3]=midp[2] + (midp[3]-midp[2])/2`
`brk[length(midpoints)+1]=midp[length(midpoints)] + margin`
where `margin=(midp[2]-midp[1])/2`.
In general, the break point is located at the center of two midpoints:
`brk[k]=0.5*(midp[k-1]+midp[k])`

Midpoint values from break values:
`midp[1]=0.5*(brk[1]+brk[2])` or midp[1]=min
`midp[2]=0.5*(brk[2]+brk[3])`
`midp[3]=2*brk[3]-midp[2]`
`brk[length(brk)-1]=2*brk[length(brk)-1]-midp[length(brk)-2]`

Note that midp[1] is treated separately and it is assumed that the break point is located at the center of two midpoints.

Try below to see how the obs on the border are classified.
` xx <- c(1,2,3,4,5,6,7) `
` brks <- c(0,2,4,6,8) `
` cc1 <- cut(xx,brks) `
` cc2 <- cut(xx,brks, right=FALSE) `
` Print(xx,as.character(cc1),as.character(cc2)) `

### Value

A vector of midpoints of length length(brk)-1.

### Examples

```midp <- c(0,1,2,4,6,9,10,11)
brk <- midp2brk( midp )
Print( midp, brk, brk2midp(brk) )
brk[1] <- -4
Print( midp, brk, brk2midp(brk) )

```

[Package lazy.tools version 0.1.3 Index]