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rworkshop8 [2014/11/03 04:07] johannabradie [Loop Modifications] |
rworkshop8 [2014/11/03 16:18] (current) johannabradie |
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| </code> | </code> | ||
| - | Curly brackets { } are used so that R knows to expect more input. When using brackets, R waits to evaluate the command until the brackets have been closed. | + | Curly brackets { } are used so that R knows to expect more input. When using brackets, R waits to evaluate the command until the brackets have been closed. If the curly brackets are not used, R may not behave as you are expecting. For example, try: |
| - | + | ||
| - | If the curly brackets are not used, R may not behave as you are expecting. For example, try: | + | |
| <code rsplus> | <code rsplus> | ||
| Line 82: | Line 80: | ||
| } # Since all brackets are now closed, R will evaluate the commands. | } # Since all brackets are now closed, R will evaluate the commands. | ||
| </code> | </code> | ||
| + | |||
| + | Note that if and if/else test a single condition. If you want to test a vector of conditions (and get a vector of results), you can use ifelse: | ||
| + | |||
| + | For example, | ||
| + | <code rsplus> | ||
| + | a<-1:10 | ||
| + | ifelse(a>5,"yes","no") | ||
| + | </code> | ||
| + | |||
| + | You can also use ifelse in a function to apply a function only under certain conditions: | ||
| + | |||
| + | |||
| + | For example, | ||
| + | <code rsplus> | ||
| + | a<-(-4):5 | ||
| + | sqrt(ifelse(a>=0,a,NA)) | ||
| + | </code> | ||
| + | |||
| + | **Exercise** | ||
| + | |||
| + | <code rsplus> | ||
| + | Paws<-"cat" | ||
| + | Scruffy<-"dog" | ||
| + | Sassy<-cat | ||
| + | animals<-c(Paws,Scruffy,Sassy) | ||
| + | </code> | ||
| + | |||
| + | 1. Use an if statement to print "meow" if Paws is a "cat". | ||
| + | |||
| + | <hidden> | ||
| + | <code rsplus> | ||
| + | if(Paws=="cat") { | ||
| + | print("meow")} | ||
| + | </code> | ||
| + | </hidden> | ||
| + | |||
| + | 2. Use an if/else statement to print "woof" if you supply an object that is a "dog" and "meow" if it is not. Try it out with Paws and Scruffy. | ||
| + | |||
| + | |||
| + | <hidden> | ||
| + | <code rsplus> | ||
| + | if(Scruffy=="dog") { | ||
| + | print("woof") | ||
| + | } else { | ||
| + | print ("meow") | ||
| + | } | ||
| + | |||
| + | if(Paws=="dog") { | ||
| + | print("woof") | ||
| + | } else { | ||
| + | print ("meow") | ||
| + | } | ||
| + | </code> | ||
| + | </hidden> | ||
| + | |||
| + | 3. Use an ifelse statement to display "woof" for animals that are dogs and "meow" for animals that are cats. | ||
| + | |||
| + | <hidden> | ||
| + | <code rsplus> | ||
| + | ifelse(animals=="dog","woof","meow") | ||
| + | </code> | ||
| + | </hidden> | ||
| + | |||
| ==== Loops ==== | ==== Loops ==== | ||
| Line 147: | Line 208: | ||
| } | } | ||
| </file> | </file> | ||
| - | |||
| The expression part of the loop can be almost anything and is usually a compound statement containing many commands. | The expression part of the loop can be almost anything and is usually a compound statement containing many commands. | ||
| Line 162: | Line 222: | ||
| //while loops// and //repeat loops// operate similarly to //for loops//. Once you understand how //for loops// work, you should be able to use any type of loop. You will see some examples of //while loops// and //repeat loops// in the next section. | //while loops// and //repeat loops// operate similarly to //for loops//. Once you understand how //for loops// work, you should be able to use any type of loop. You will see some examples of //while loops// and //repeat loops// in the next section. | ||
| + | |||
| + | **Exercise** | ||
| + | |||
| + | NEED TO WRITE IN AN EXERCISE | ||
| ==== Loop Modifications ==== | ==== Loop Modifications ==== | ||
| Line 209: | Line 273: | ||
| </file> | </file> | ||
| - | Using flow control to make a complex plot | + | **Exercise** |
| + | |||
| + | NEED TO WRITE IN AN EXERCISE | ||
| + | |||
| + | **Using flow control to make a complex plot** | ||
| The idea here is that we have a dataset we want to plot, with concentration and uptake values, but each point has a type (Quebec or Mississippi) and a treatment ("chilled" or "nonchilled") and we want to plot the points differently for these cases. | The idea here is that we have a dataset we want to plot, with concentration and uptake values, but each point has a type (Quebec or Mississippi) and a treatment ("chilled" or "nonchilled") and we want to plot the points differently for these cases. | ||
| Line 238: | Line 306: | ||
| </file> | </file> | ||
| + | |||
| + | **Exercise** | ||
| + | |||
| + | NEED TO WRITE IN AN EXERCISE | ||
| <file rsplus> | <file rsplus> | ||
| </file> | </file> | ||
