How we can print array variable in log file of Magento 2?

Suppose your array is

$a = array ('a' => 'apple', 'b' => 'banana', 'c' => array ('x', 'y', 'z'));

then you have to write below code to write proper array format in your log file

$this->_logger->log(100,print_r($a,true));

It will print in you log file

[2015-11-09 06:58:27] main.DEBUG: Array
(
    [a] => apple
    [b] => banana
    [c] => Array
        (
            [0] => x
            [1] => y
            [2] => z
        )

)
 {"is_exception":false} []

See declaration of log method

public function  \Psr\Log\LoggerInterface::log($level, $message, array $context = array());

So, you need code like

$this->_logger->log(100, json_encode($options));

This method works well for me.

$this->logger->info(print_r($myArray, true));

Then check your system.log file.