# Bioimage Analysis Wiki

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documents:111012rtricks

# R Tricks

## removing trailing zeros from a vector

When you import data from the out put of other software, you might have trailing 0s at the end of each column:

> d0
[1] 69.444 70.889 86.667 95.667 83.444 78.333 67.889
[8] 56.000 49.222 40.333 37.889 31.889 30.333 26.667
[15] 22.444 23.111 20.889 22.000 20.111 19.778 20.778
[22] 19.667 17.333 19.333 19.000 16.333 14.444 13.889
[29] 18.000 21.778 23.556 23.889 28.778 40.000 48.667
[36] 55.889 66.667 78.889 72.222 84.778 68.778 69.444
[43]  0.000  0.000  0.000  0.000  0.000  0.000  0.000
[50]  0.000  0.000  0.000  0.000  0.000  0.000  0.000
[57]  0.000  0.000  0.000  0.000  0.000  0.000  0.000
[64]  0.000  0.000  0.000  0.000


To remove them, there could be many ways, but here is my one liner.

d0c <- d0[rev(cumsum(rev(d0)))>0]


Then the output is

> d0c
[1] 69.444 70.889 86.667 95.667 83.444 78.333 67.889
[8] 56.000 49.222 40.333 37.889 31.889 30.333 26.667
[15] 22.444 23.111 20.889 22.000 20.111 19.778 20.778
[22] 19.667 17.333 19.333 19.000 16.333 14.444 13.889
[29] 18.000 21.778 23.556 23.889 28.778 40.000 48.667
[36] 55.889 66.667 78.889 72.222 84.778 68.778 69.444


## Plotting a matrix data as a color-coded image

#a 2Dplot, color coded.
x <- c(1:20)
y <- c(1:10)
for(j in y){
for(i in x){
val <- i+j
if((i == 0) & (j == 0)) z <- val
elsez <- append(z, val)
}
}

z <- matrix(z, nrow=20, ncol=10)
mat <- list(x, y, z)
image(x, y, z)

Example plotting of a matrix using base graphics function image()

… a bit faster way calculation wise uses indexing.

width <- 10
height <- 20
x <- c(1:width)
y <- c(1:height)
xindex <-rep(x, length = width*height)
yindex <- yindexing(x, y)

z <- xindex + yindex

z <- matrix(z, nrow=width, ncol=height)
mat <- list(x, y, z)
image(x, y, z)

yindexing <- function (x, y) {
for(i in y){
cr <- rep(i, length=length(x))
if (i==1) all <- cr
else all <- append(all, cr)
}
return (all)
}


## Inserting math formula & symbols in label or title

The easiest way is to use function expression(). For example,

plot(back\$V2, type='l', xlab=expression(slice %.% time), ylab='intensity', xaxt="n", yaxt="n")


Inserts vertically centered dot in the x label between “slice” and “time”. You could check other available expressions by

?plotmath


More recent, but under development is using tikzDevice.

## Variable Name to String

myfunc <- function(v1) {
deparse(substitute(v1))
}

myfunc(foo)
[1] "foo"