select previous item in twig for loop - for-loop

Question

I use twig and have some data in array. I use for loop to access all data like this:
{% for item in data %}
Value : {{ item }}
{% endfor %}
Is it possible to access previous item in loop? For example: when I'm on n item, I want to have access to n-1 item.

Answer 1

There's no built-in way to do that, but here's a workaround:
{% set previous = false %}
{% for item in data %}
Value : {{ item }}
{% if previous %}
{# use it #}
{% endif %}
{% set previous = item %}
{% endfor %}
The if is neccessary for the first iteration.

Answer 2

In addition to #Maerlyn 's example, here is code to provide for next_item (the one after current one)
{# this template assumes that you use 'items' array
and each element is called 'item' and you will get
'previous_item' and 'next_item' variables, which may be NULL if not availble #}
{% set previous_item = null %}
{%if items|length > 1 %}
{% set next_item = items[1] %}
{%else%}
{% set next_item = null %}
{%endif%}
{%for item in items %}
Item: {{ item }}
{% if previous_item is not null %}
Use previous item here: {{ previous_item }}
{%endif%}
{%if next_item is not null %}
Use next item here: {{ next_item }}
{%endif%}
{# ------ code to udpate next_item and previous_item elements #}
{%set previous_item = item %}
{%if loop.revindex <= 2 %}
{% set next_item = null %}
{%else%}
{% set next_item = items[loop.index0+2] %}
{%endif%}
{%endfor%}

Answer 3

My solution:
{% for item in items %}
<p>item itself: {{ item }}</p>
{% if loop.length > 1 %}
{% if loop.first == false %}
{% set previous_item = items[loop.index0 - 1] %}
<p>previous item: {{ previous_item }}</p>
{% endif %}
{% if loop.last == false %}
{% set next_item = items[loop.index0 + 1] %}
<p>next item: {{ next_item }}</p>
{% endif %}
{% else %}
<p>There is only one item.</p>
{% endif %}
{% endfor %}
I had to make endless image gallery where before first item goes last one and after last item goes first one. It could be done this way:
{% for item in items %}
<p>item itself: {{ item }}</p>
{% if loop.length > 1 %}
{% if loop.first %}
{% set previous_item = items[loop.length - 1] %}
{% else %}
{% set previous_item = items[loop.index0 - 1] %}
{% endif %}
{% if loop.last %}
{% set next_item = items[0] %}
{% else %}
{% set next_item = items[loop.index0 + 1] %}
{% endif %}
<p>previous item: {{ previous_item }}</p>
<p>next item: {{ next_item }}</p>
{% else %}
<p>There is only one item.</p>
{% endif %}
{% endfor %}