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--- documents:111012rtricks [2012/06/13 12:38] – kota
+++ documents:111012rtricks [2012/07/11 15:10] – external edit 127.0.0.1
@@ Line 1: / Line 1: @@
-====== 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:
-<code>
-> 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
-</code>
-To remove them, there could be many ways, but here is my one liner.
-<code R>
-d0c <- d0[rev(cumsum(rev(d0)))>0]
-</code>
-Then the output is
-<code>
-> 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
-</code>
-===== Plotting a matrix data as a color-coded image =====
-<sxh>
-#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)
-</sxh>
-[{{:documents:rtips:imageplot.png| Example plotting of a matrix using base graphics function image()}}]
-... a bit faster way calculation wise uses indexing.
-<sxh>
-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)
-}
-</sxh>
-===== Inserting math formula & symbols in label or title =====
-The easiest way is to use function //expression()//. For example,
-<code>
-plot(back$V2, type='l', xlab=expression(slice %.% time), ylab='intensity', xaxt="n", yaxt="n")
-</code>
-Inserts vertically centered dot in the x label between "slice" and "time". You could check other available expressions by
-<code>
-?plotmath
-</code>
-More recent, but under development is using [[http://cran.r-project.org/web/packages/tikzDevice/|tikzDevice]].