# Replace.im

##### Reset Values in Subset of Image

Reset the values in a subset of a pixel image.

##### Usage

```
# S3 method for im
[(x, i, j, …, drop=TRUE) <- value
```

##### Arguments

- x
A two-dimensional pixel image. An object of class

`"im"`

.- i
Object defining the subregion or subset to be replaced. Either a spatial window (an object of class

`"owin"`

), or a pixel image with logical values, or a point pattern (an object of class`"ppp"`

), or any type of index that applies to a matrix, or something that can be converted to a point pattern by`as.ppp`

(using the window of`x`

).- j
An integer or logical vector serving as the column index if matrix indexing is being used. Ignored if

`i`

is appropriate to some sort of replacement*other than*matrix indexing.- …
Ignored.

- drop
Logical value specifying what happens when

`i`

and`j`

are both missing. See Details.- value
Vector, matrix, factor or pixel image containing the replacement values. Short vectors will be recycled.

##### Details

This function changes some of the pixel values in a
pixel image. The image `x`

must be an object of class
`"im"`

representing a pixel image defined inside a
rectangle in two-dimensional space (see `im.object`

).

The subset to be changed is determined by the arguments `i,j`

according to the following rules (which are checked in this order):

`i`

is a spatial object such as a window, a pixel image with logical values, or a point pattern; or`i,j`

are indices for the matrix`as.matrix(x)`

; or`i`

can be converted to a point pattern by`as.ppp(i, W=Window(x))`

, and`i`

is not a matrix.

If `i`

is a spatial window (an object of class `"owin"`

),
the values of the image inside this window are changed.

If `i`

is a point pattern (an object of class
`"ppp"`

), then the values of the pixel image at the points of
this pattern are changed.

If `i`

does not satisfy any of the conditions above, then
the algorithm tries to interpret `i,j`

as indices for the matrix
`as.matrix(x)`

. Either `i`

or `j`

may be missing or blank.

If none of the conditions above are met, and if `i`

is not
a matrix, then `i`

is converted into a point pattern
by `as.ppp(i, W=Window(x))`

.
Again the values of the pixel image at the points of
this pattern are changed.

If `i`

and `j`

are both missing, as in the call
`x[] <- value`

, then all pixel values in `x`

are replaced by `value`

:

If

`drop=TRUE`

(the default), then this replacement applies only to pixels whose values are currently defined (i.e. where the current pixel value is not`NA`

). If`value`

is a vector, then its length must equal the number of pixels whose values are currently defined.If

`drop=FALSE`

then the replacement applies to all pixels inside the rectangle`Frame(x)`

. If`value`

is a vector, then its length must equal the number of pixels in the entire rectangle.

##### Value

The image `x`

with the values replaced.

##### Warning

If you have a 2-column matrix containing the \(x,y\) coordinates
of point locations, then to prevent this being interpreted as an
array index, you should convert it to a `data.frame`

or to a point pattern.

##### See Also

##### Examples

```
# NOT RUN {
# make up an image
X <- setcov(unit.square())
plot(X)
# a rectangular subset
W <- owin(c(0,0.5),c(0.2,0.8))
X[W] <- 2
plot(X)
# a polygonal subset
data(letterR)
R <- affine(letterR, diag(c(1,1)/2), c(-2,-0.7))
X[R] <- 3
plot(X)
# a point pattern
P <- rpoispp(20)
X[P] <- 10
plot(X)
# change pixel value at a specific location
X[list(x=0.1,y=0.2)] <- 7
# matrix indexing --- single vector index
X[1:2570] <- 10
plot(X)
# matrix indexing using double indices
X[1:257,1:10] <- 5
plot(X)
# matrix indexing using a matrix of indices
X[cbind(1:257,1:257)] <- 10
X[cbind(257:1,1:257)] <- 10
plot(X)
# Blank indices
Y <- as.im(letterR)
plot(Y)
Y[] <- 42 # replace values only inside the window 'R'
plot(Y)
Y[drop=FALSE] <- 7 # replace all values in the rectangle
plot(Y)
Z <- as.im(letterR)
Z[] <- raster.x(Z, drop=TRUE) # excludes NA
plot(Z)
Z[drop=FALSE] <- raster.y(Z, drop=FALSE) # includes NA
plot(Z)
# }
```

*Documentation reproduced from package spatstat, version 1.64-1, License: GPL (>= 2)*