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. 
 
for(j in seq(0, 9)){
  for(i in seq(0, 19)){
    val <- i+j
    if((i == 0) & (j == 0)) {
      z <- val    
    } else {
      z <- append(z, val)
    }
  }
}
x <- c(1:20)
y <- c(1:10)  
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()