Struggling with simple Groovy List operations - list

Question

I've abstracted a very simple situation here, in which I want to pass a list of strings into my cleanLines function and get a list of strings back out. Unfortunately, I'm new to Groovy and I've spent about a day trying to get this to work with no avail. Here's a stand-alone test that exhibits the problem I'm having:
import static org.junit.Assert.*;
import java.util.List;
import org.junit.Test;
class ConfigFileTest {
private def tab = '\t'
private def returnCarriage = '\r'
private def equals = '='
List <String> cleanLines(List <String> lines) {
lines = lines.collect(){it.findAll(){c -> c != tab && c != returnCarriage}}
lines = lines.findAll(){it.contains(equals)}
lines = lines.collect{it.trim()}
}
#Test
public void test() {
List <String> dirtyLines = [" Colour=Red",
"Shape=Square "]
List <String> cleanedLines = ["Colour=Red",
"Shape=Square"]
assert cleanLines(dirtyLines) == cleanedLine
}
}
I believe that I've followed the correct usage for collect(), findAll() and trim(). But when I run the test, it crashes on the trim() line stating
groovy.lang.MissingMethodException: No signature of method:
java.util.ArrayList.trim() is applicable for argument types: ()
values: []
. Something's suspicious.
I've been staring at this for too long and noticed that my IDE thinks the type of my first lines within the cleanLines function is List<String>, but that by the second line it has type Collection and by the third it expects type List<Object<E>>. I think that String is an Object and so this might be okay, but it certainly hints at a misunderstanding on my part. What am I doing wrong? How can I get my test to pass here?

Answer 1

Here's a corrected script:
import groovy.transform.Field
#Field
def tab = '\t'
#Field
def returnCarriage = '\r'
#Field
def equals = '='
List <String> cleanLines(List <String> lines) {
lines = lines.findAll { it.contains(equals) }
lines = lines.collect { it.replaceAll('\\s+', '') }
lines = lines.collect { it.trim() }
}
def dirtyLines = [" Colour=Red",
"Shape=Square "]
def cleanedLines = ["Colour=Red", "Shape=Square"]
assert cleanLines(dirtyLines) == cleanedLines
In general findAll and collect are maybe not mutually exclusive but have different purposes. Use findAll to find elements that matches certain criteria, whereas collect when you need to process/transform the whole list.

Answer 2

this line
lines = lines.collect(){it.findAll(){c -> c != tab && c != returnCarriage}}`
replaces the original list of Strings with the list of lists. Hence NSME for ArrayList.trim(). You might want to replace findAll{} with find{}

Answer 3

You can clean the lines like this:
def dirtyLines = [" Colour=Red", "Shape=Square "]
def cleanedLines = ["Colour=Red", "Shape=Square"]
assert dirtyLines.collect { it.trim() } == cleanedLines

Answer 4

If you separate the first line of cleanLines() into two separate lines and print lines after each, you will see the problem.
it.findAll { c -> c != tab && c != returnCarriage }
will return a list of strings that match the criteria. The collect method is called on every string in the list of lines. So you end up with a list of lists of strings. I think what you are looking for is something like this:
def cleanLines(lines) {
return lines.findAll { it.contains(equals) }
.collect { it.replaceAll(/\s+/, '') }
}