通過在Python中使用combinebykey spark rdd來計算組中的聚合（pyspark）

Question

我是新的spark rdd，我想使用spark shuffling操作通過按鍵對它們進行分組來計算聚合。 起初，我的方法是使用rdd.groupby()，但在執行時需要較長的時間才能收斂並且內存非常有效，但我知道這種操作在混洗方面成本很高。 我碰到另一個操作rdd.combinebykey()但我在理解和使用它時遇到問題。

這是存儲在RDD我的數據稱其爲

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warhorses. final, regular foxes integrate carefully. bold packages nag blithely ev', u''), (u'84', u'Customer#000000084', u'lpXz6Fwr9945rnbtMc8PlueilS1WmASr CB', u'11', u'21-546-818-3802', u'5174.71', u'FURNITURE', u'ly blithe foxes. special asymptotes haggle blithely against the furiously regular depo', u''), (u'85', u'Customer#000000085', u'siRerlDwiolhYR 8FgksoezycLj', u'5', u'15-745-585-8219', u'3386.64', u'FURNITURE', u'ronic ideas use above the slowly pendin', u''), (u'86', u'Customer#000000086', u'US6EGGHXbTTXPL9SBsxQJsuvy', u'0', u'10-677-951-2353', u'3306.32', u'HOUSEHOLD', u'quests. pending dugouts are carefully aroun', u''), (u'87', u'Customer#000000087', u'hgGhHVSWQl 6jZ6Ev', u'23', u'33-869-884-7053', u'6327.54', u'FURNITURE', u'hely ironic requests integrate according to the ironic accounts. slyly regular pla', u''), (u'88', u'Customer#000000088', u'wtkjBN9eyrFuENSMmMFlJ3e7jE5KXcg', u'16', u'26-516-273-2566', u'8031.44', u'AUTOMOBILE', u's are quickly above the quickly ironic instructions; even requests about the carefully final deposi', u''), (u'89', u'Customer#000000089', u'dtR, y9JQWUO6FoJExyp8whOU', u'14', u'24-394-451-5404', u'1530.76', u'FURNITURE', u'counts are slyly beyond the slyly final accounts. quickly final ideas wake. r', u''), (u'90', u'Customer#000000090', u'QxCzH7VxxYUWwfL7', u'16', u'26-603-491-1238', u'7354.23', u'BUILDING', u'sly across the furiously even ', u''), (u'91', u'Customer#000000091', u'S8OMYFrpHwoNHaGBeuS6E 6zhHGZiprw1b7 q', u'8', u'18-239-400-3677', u'4643.14', u'AUTOMOBILE', u'onic accounts. fluffily silent pinto beans boost blithely according to the fluffily exp', u''), (u'92', u'Customer#000000092', u'obP PULk2LH LqNF,K9hcbNqnLAkJVsl5xqSrY,', u'2', u'12-446-416-8471', u'1182.91', u'MACHINERY', u'. pinto beans hang slyly final deposits. ac', u''), (u'93', u'Customer#000000093', u'EHXBr2QGdh', u'7', u'17-359-388-5266', u'2182.52', u'MACHINERY', u'press deposits. carefully regular platelets r', u''), (u'94', u'Customer#000000094', u'IfVNIN9KtkScJ9dUjK3Pg5gY1aFeaXewwf', u'9', u'19-953-499-8833', u'5500.11', u'HOUSEHOLD', u'latelets across the bold, final requests sleep according to the fluffily bold accounts. unusual deposits amon', u''), (u'95', u'Customer#000000095', u'EU0xvmWvOmUUn5J,2z85DQyG7QCJ9Xq7', u'15', u'25-923-255-2929', u'5327.38', u'MACHINERY', u'ithely. ruthlessly final requests wake slyly alongside of the furiously silent pinto beans. even the', u''), (u'96', u'Customer#000000096', u'vWLOrmXhRR', u'8', u'18-422-845-1202', u'6323.92', u'AUTOMOBILE', u'press requests believe furiously. carefully final instructions snooze carefully. ', u''), (u'97', u'Customer#000000097', u'OApyejbhJG,0Iw3j rd1M', u'17', u'27-588-919-5638', u'2164.48', u'AUTOMOBILE', u'haggle slyly. bold, special ideas are blithely above the thinly bold theo', u''), (u'98', u'Customer#000000098', u'7yiheXNSpuEAwbswDW', u'12', u'22-885-845-6889', u'-551.37', u'BUILDING', u'ages. furiously pending accounts are quickly carefully final foxes: busily pe', u''), (u'99', u'Customer#000000099', u'szsrOiPtCHVS97Lt', u'15', u'25-515-237-9232', u'4088.65', u'HOUSEHOLD', u'cajole slyly about the regular theodolites! furiously bold requests nag along the pending, regular packages. somas', u''), (u'100', u'Customer#000000100', u'fptUABXcmkC5Wx', u'20', u'30-749-445-4907', u'9889.89', u'FURNITURE', u'was furiously fluffily quiet deposits. silent, pending requests boost against ', u'')] 

我申請GROUPBY（「customerrdd」）在attribute key-6進一步customerrdd， 對砂石料的操作說addition on attribute key-3本人已應用了一系列reducebykey操作flatmap和mapling值，這裏是它的代碼：

def func(x): 
    return x 


def stringconverfunc(z): 
    return str(z) 


def floatconverfunc(l): 
    return float(l) 

def aggonvalfunc(y): 
    return y[3] 


grouprdd=customerrdd.groupBy(lambda w:(w[6])) 


result=grouprdd.flatMapValues(lambda q: func(q)).mapValues(lambda p: aggonvalfunc(p)) \ 
     .mapValues(lambda line: stringconverfunc(line)).mapValues(lambda line: line.strip()) \ 
     .mapValues(lambda line: floatconverfunc(line)).reduceByKey(lambda x, y: x + y).collect() 
print result 

OUTPUT：

[(u'BUILDING', 20), (u'AUTOMOBILE', 21), (u'HOUSEHOLD', 21), (u'MACHINERY', 16), (u'FURNITURE', 22)] 

但是，上述方法在混洗方面相當昂貴，並且不適用於較大的數據集。因此，我想用rdd.combinebykey來實現上述相同的概念，以便更快地計算並可用於較大的數據集。 我試圖通過引用combinebykey來實現它，但卻很困惑如何提供需要執行聚合的密鑰和值。誰能幫忙？我想提出建議

Answer 1

好的，對於初學者來說很難知道所有這些，所以我會盡量給你一些提示。

您可以分配鍵而不分組，這可以通過keyBy來完成，並且不涉及洗牌。最後，一個鍵值rdd僅僅是一個由大小爲2的元組組成的rdd，其中第一個鍵是鍵，第二個鍵是值。
從reduceByKey或combineByKey可以獲得的任何性能提升將會變得無用，如果您事先進行了分組，則可以避免這種情況。

此外，您可以調用float使用具有前導和尾隨空格的字符串，它會自動剝離字符串。您也不需要創建形式爲lambda x: f(x)的lambdas，只需使用f而不需要任何大括號，它將具有相同的效果。出於同樣的原因，您不需要將str或float換成其他功能。
operator模塊提供了添加和檢索值的功能，因此您不需要定義這些值。請查看python文檔以獲取更多信息。

我的解決辦法是：

from operator import itemgetter, add 

# `itemgetter(6)` is equivalent to `lambda x: x[6]`. Therefore we'll use element at 
# index 6 to key the rdd's entries. 
# This operation is equivalent to `customerrdd.map(lambda x: (x[6], x))` 
rdd = customerrdd.keyBy(itemgetter(6)) 

# Now extract element at index 3 from the values so we no longer have a tuple 
rdd = rdd.mapValues(itemgetter(3)) 

# Convert those elements to floats 
rdd = rdd.mapValues(float) 

# We could've done the previous steps in one by doing 
# rdd = customerrdd.map(lambda x: (x[6], float(x[3])) 

# Sum them up and collect the result 
result = rdd.reduceByKey(add).collect() 

沒有評論

from operator import itemgetter, add 

result = customerrdd.keyBy(itemgetter(6))\ 
    .mapValues(itemgetter(3))\ 
    .mapValues(float)\ 
    .reduceByKey(add).collect() 

這誠然返回

[(u'BUILDING', 204.0), 
(u'AUTOMOBILE', 280.0), 
(u'MACHINERY', 135.0), 
(u'HOUSEHOLD', 255.0), 
(u'FURNITURE', 224.0)] 

不同的結果比你，但我跑了你的代碼，並得到了相同的。所以我想你的結果有不同的rdd。