Apache pig 猪：从右边算位置？

我的猪脚本中有一个元组：

((,v1,fb,fql))

---

我知道我可以从左边选择$0（空白）、$1（“v1”）等元素，但我可以从右边选择元素吗？元组的长度不同，但我始终希望得到最后一个元素

你不能。但是，您可以编写python UDF来提取它：

# Make sure to include the appropriate ouputSchema
def getFromBack(TUPLE, pos):
    # gets elements from the back of TUPLE 
    # You can also do TUPLE[-pos], but this way it starts at 0 which is closer
    # to Pig
    return TUPLE[::-1][pos]

    # This works the same way as above, but may be faster
    # return TUPLE[-(pos + 1)]

用起来像：

register 'myudf.py' using jython as pythonUDFs ;

B = FOREACH A GENERATE pythonUDFs.getFromBack(T, 0) ;