CODEWITHSUNDEEP
groovy
Deepti
Deepti

Reputation: 461

How to Add item to start of list using Groovy?

How can I use Groovy to add an item to the beginning of a list?

Upvotes: 46

Views: 43767

Answers (4)

mike rodent
mike rodent

Reputation: 15692

Caution!

From Groovy 2.5:

list.push( myObject )

Prior to Groovy 2.5 list.push appends ... but from 2.5/2.6 (not yet Beta) it will (it seems) prepend, "to align with Java"... indeed, java.util.Stack.push has always prepended.

In fact this push method does not belong to List, but to GDK 2.5 DefaultGroovyMethods, signature <T> public static boolean push(List<T> self, T value). However, because of Groovy syntax magic we shall write as above: list.push( myObject ).

Upvotes: 9

bezmax
bezmax

Reputation: 26142

list.add(0, myObject);

You can also read this for some other valuable examples: http://groovy.codehaus.org/JN1015-Collections

Upvotes: 54

Martin Rugadya
Martin Rugadya

Reputation: 614

def list = [4, 3, 2, 1, 0]

list.plus(0, 5)

assert list == [5, 4, 3, 2, 1, 0]

You can find more examples at this link

Upvotes: 5

helpermethod
helpermethod

Reputation: 62254

Another option would be using the spread operator * which expands a list into its elements:

def list = [2, 3]
def element = 1

assert [element, *list] == [1, 2, 3]

Another alternative would be to put the element into a list and concatenate the two lists:

assert [element] + list == [1, 2, 3]​

Upvotes: 26

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