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--- documents:111012rtricks [2012/07/11 15:10] – external edit 127.0.0.1
+++ documents:111012rtricks [2020/11/26 07:08] (current) – kota
@@ 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:R>
+> 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 =====
+<code:R>
+#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)
+</code>
+[{{:documents:rtips:imageplot.png| Example plotting of a matrix using base graphics function image()}}]
+... a bit faster way calculation wise uses indexing.
+<code:R>
+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)
+}
+</code>
+===== 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]].
+===== Variable Name to String =====
+<code>
+myfunc <- function(v1) {
+  deparse(substitute(v1))
+}
+myfunc(foo)
+[1] "foo"
+</code>