Change Index Key to Name - php

Question

I have built a multidimensional array for usage in a custom Wordpress query. Although it is Wordpress I feel that this is more a basic PHP question.
The array that I have now outputs everything properly, accept for the index value. I need it to be a string instead of an integer.
Here is what I need my ouput to be
Array (
[post_type] => property
[posts_per_page] => -1
[tax_query] => Array (
[0] => Array (
[taxonomy] => state
[field] => slug
[terms] => illinois
)
[1] => Array (
[taxonomy] => illinois_county
[field] => slug
[terms] => fulton
)
)
)
And here is what is actually being output
Array (
[post_type] => property
[posts_per_page] => -1
[0] => Array (
[0] => Array (
[taxonomy] => state
[field] => slug
[terms] => illinois
)
[1] => Array (
[taxonomy] => illinois_county
[field] => slug
[terms] => fulton
)
)
)
The only difference being the key of the second array which is 0 in mine and needs to be tax_query.
To get this Array I am declaring $tax_query_array = array(); and then dropping my child arrays as needed depending on what variables are present in the url, such as $tax_query_array[] = $state_array; and $tax_query_array[] = $county_array;. Then finally calling $tax_query_array where i need the final multidimensional array output.
Only thing stopping me is the initial [0] which needs to instead be [tax_query].
Here is the full code:
$tax_query_array = array();
$tax_query_array['tax_query'][] = $state_array;
$tax_query_array['tax_query'][] = $county_array;
$tax_query_array['tax_query'][] = $price_range_array;
$taxonomy_args = array(
'post_type' => 'property',
'posts_per_page' => -1,
$tax_query_array
}
Output from changing $tax_query_array[] = $county_array; to $tax_query_array['tax_query'][] = $county_array; via MikeBrant:
Array (
[post_type] => property
[posts_per_page] => -1
[0] => Array (
[tax_query] => Array (
[0] => Array (
[taxonomy] => state
[field] => slug
[terms] => illinois
)
[1] => Array (
[taxonomy] => illinois_county
[field] => slug
[terms] => fulton
)
)
)
)

Answer 1

Try this code:
$taxonomy_args = array(
'post_type' => 'property',
'posts_per_page' => -1,
'tax_query'=> array($state_array, $county_array, $price_range_array)
}