![if() statement inside for-loop
Avoid using the for-loop
variable in an if-condition
for(g in genes) {
if ( data[g, 'strand'] == '-') {
data[g, 'len' ] <- -data[g, 'len']
}
}
It’s often a sign that things can
be simplified using vector
notation:
rev <- data[genes, 'strand'] == '-'
data[rev , 'len' ] <- -data[rev, 'len' ]](https://image.slidesharecdn.com/day5a-iterationandfunctionsif-171210233052/85/Day-5a-iteration-and-functions-if-pptx-5-320.jpg)
Day 5a iteration and functions if().pptx
- 1. Iteration and functions: if() Day 5a - Introduction to R for Life Sciences
- 2. if() (and else) if( some.condition ) { # do stuff } some.condition is simply a single-valued logical. As with functions, and for-loops: indent, and use curly braces if ( some.condition) { # do stuff } else { # do other stuff }
- 3. if Conditions often look like if( a > b ) { … } But you can also use logicals: if ( print.to.file ) { … } Never write: if (print.to.file == TRUE) { … } Nor: if ( adjust.pvalues == FALSE ) { … }. Instead, write if (! adjust.pvalues) { … }
- 4. Condition must be a single value if (big.vector) { do.stuff() } Warning message: In if (big.vector) { do.stuff() } : the condition has length > 1 and only the first element will be used Use aggregate functions such as any() or all() Inside if(), prefer && and || for logical AND and logical OR (as opposed to & and | )
- 5. if() statement inside for-loop Avoid using the for-loop variable in an if-condition for(g in genes) { if ( data[g, 'strand'] == '-') { data[g, 'len' ] <- -data[g, 'len'] } } It’s often a sign that things can be simplified using vector notation: rev <- data[genes, 'strand'] == '-' data[rev , 'len' ] <- -data[rev, 'len' ]
- 6. The End
- 7. && and || They work on only the first element (and silently ignore the rest) They short-circuit: only as many as needed are evaluated: if( is.null(s) || s=="" ) { # double bar stop("string missing") } There may be no first element: > s<-NULL > s=="" logical(0) > if( is.null(s) | s=="" ) { # single bar stop("string missing") } Error in if (is.null(s) | s == "") { : argument is of length zero
- 8. The triple-dot The triple dot (…) collects ‘the rest’ of the arguments Inside the function, this ‘rest’ can be passed on to other calls (provided those functions take triple-dot arguments) Warns about arguments that never get used This magically endows your function with extra arguments Often used for plotting functions: main, sub, xlab,ylab, xlim, ylim, ...
- 9. Example my.plot <- function(x, ...) { plot(density(x), ...) rug(x, ...) } my.plot(x, main="slx5", xlab="M", col="red", xlim=c(-4,4), lwd=2, ticksize= -0.02) Warning messages: 1: In plot.window(...) : "ticksize" is not a graphical parameter 2: In plot.xy(xy, type, ...) : "ticksize" is not a graphical parameter 3: In axis(side = side, at = at, labels = labels, ...) : "ticksize" is not a graphical parameter 4: In axis(side = side, at = at, labels = labels, ...) : "ticksize" is not a graphical parameter 5: In box(...) : "ticksize" is not a graphical parameter 6: In title(...) : "ticksize" is not a graphical parameter