如何从元组列表中提取包含元素的元组？答案

【问题标题】：How to extract a tuple that contains an element from tuple list?如何从元组列表中提取包含元素的元组？
【发布时间】：2016-07-02 18:53:45
【问题描述】：

我有这个元组列表：

[{denomination_flexible_denomination,236,9,2,"1","CORE BALANCE",0,10,"1","500","100","100",null,"ecrlrlep_facilito","ecrlrlep_facilito","true","[{codigo_producto, \"0010701020\"}, {tipo_trx_pago, \"10220\"}, {tipo_trx_consulta, \"310220\"}, {payment_type, \"electronic_money\"}]"},
 {denomination_flexible_denomination,239,8,2,"2","CORE BALANCE",0,10,"1","500","100","100",null,"ecrlrlep_facilito","ecrlrlep_facilito","true","[{codigo_producto, \"0010701020\"}, {tipo_trx_pago, \"10120\"}, {tipo_trx_consulta, \"310120\"}, {payment_type, \"electronic_money\"}]"}]

我需要提取包含 denomination_flexible_denomination 239 的元组。有人知道该怎么做吗？

【问题讨论】：

标签： erlang

【解决方案1】：

使用lists:keyfind/3。它的参数是键（在本例中为 239）、元组中的位置（2，因为它是第二个元组元素）和元组列表：

> lists:keyfind(239, 2, TupleList).
{denomination_flexible_denomination,239,8,2,"2",
                                    "CORE BALANCE",0,10,"1","500","100","100",null,
                                    "ecrlrlep_facilito","ecrlrlep_facilito","true",
                                    "[{codigo_producto, \"0010701020\"}, {tipo_trx_pago, \"10120\"}, {tipo_trx_consulta, \"310120\"}, {payment_type, \"electronic_money\"}]"}

如果没有匹配的元素，lists:keyfind/3 返回false。

【讨论】：

【解决方案2】：

使用lists:filter的最简单方法

TupleList = [{denomination_flexible_denomination,236,9,2,"1","CORE BALANCE",0,10,"1","500","100","100",null,"ecrlrlep_facilito","ecrlrlep_facilito","true","[{codigo_producto, \"0010701020\"}, {tipo_trx_pago, \"10220\"}, {tipo_trx_consulta, \"310220\"}, {payment_type, \"electronic_money\"}]"},{denomination_flexible_denomination,239,8,2,"2","CORE BALANCE",0,10,"1","500","100","100",null,"ecrlrlep_facilito","ecrlrlep_facilito","true","[{codigo_producto, \"0010701020\"}, {tipo_trx_pago, \"10120\"}, {tipo_trx_consulta, \"310120\"}, {payment_type, \"electronic_money\"}]"}].

R=lists:filter(fun(Tuple)->(element(1,Tuple)=:=denomination_flexible_denomination) and (element(2,Tuple)=:=239) end,TupleList).

【讨论】：

【解决方案3】：

1> L = [{denomination_flexible_denomination,236,9,2,"1","CORE BALANCE",0,10,"1","500","100","100",null,"ecrlrlep_facilito","ecrlrlep_facilito","true","[{codigo_producto, \"0010701020\"}, {tipo_trx_pago, \"10220\"}, {tipo_trx_consulta, \"310220\"}, {payment_type, \"electronic_money\"}]"},
1>  {denomination_flexible_denomination,239,8,2,"2","CORE BALANCE",0,10,"1","500","100","100",null,"ecrlrlep_facilito","ecrlrlep_facilito","true","[{codigo_producto, \"0010701020\"}, {tipo_trx_pago, \"10120\"}, {tipo_trx_consulta, \"310120\"}, {payment_type, \"electronic_money\"}]"}].
[{denomination_flexible_denomination,236,9,2,"1",
                                     "CORE BALANCE",0,10,"1","500","100","100",null,
                                     "ecrlrlep_facilito","ecrlrlep_facilito","true",
                                     "[{codigo_producto, \"0010701020\"}, {tipo_trx_pago, \"10220\"}, {tipo_trx_consulta, \"310220\"}, {payment_type, \"electronic_money\"}]"},
 {denomination_flexible_denomination,239,8,2,"2",
                                     "CORE BALANCE",0,10,"1","500","100","100",null,
                                     "ecrlrlep_facilito","ecrlrlep_facilito","true",
                                     "[{codigo_producto, \"0010701020\"}, {tipo_trx_pago, \"10120\"}, {tipo_trx_consulta, \"310120\"}, {payment_type, \"electronic_money\"}]"}]
2> [ X || {denomination_flexible_denomination, 239, _,_,_,_,_,_,_,_,_,_,_,_,_,_,_} =X <- L].            
[{denomination_flexible_denomination,239,8,2,"2",
                                     "CORE BALANCE",0,10,"1","500","100","100",null,
                                     "ecrlrlep_facilito","ecrlrlep_facilito","true",
                                     "[{codigo_producto, \"0010701020\"}, {tipo_trx_pago, \"10120\"}, {tipo_trx_consulta, \"310120\"}, {payment_type, \"electronic_money\"}]"}]

或

3> [ X || X <- L, element(1,X) =:= denomination_flexible_denomination, element(2, X) =:= 239].
[{denomination_flexible_denomination,239,8,2,"2",
                                     "CORE BALANCE",0,10,"1","500","100","100",null,
                                     "ecrlrlep_facilito","ecrlrlep_facilito","true",
                                     "[{codigo_producto, \"0010701020\"}, {tipo_trx_pago, \"10120\"}, {tipo_trx_consulta, \"310120\"}, {payment_type, \"electronic_money\"}]"}]

或

4> list_to_tuple([ list_to_atom("field_" ++ integer_to_list(X)) || X <- lists:seq(1,16) ]).
{field_1,field_2,field_3,field_4,field_5,field_6,field_7,
         field_8,field_9,field_10,field_11,field_12,field_13,
         field_14,field_15,field_16}
5> rd(denomination_flexible_denomination, v(-1)).                                               
denomination_flexible_denomination
6> [ X || #denomination_flexible_denomination{field_1 = 239} = X <- L].
[#denomination_flexible_denomination{field_1 = 239,
                                     field_2 = 8,field_3 = 2,field_4 = "2",
                                     field_5 = "CORE BALANCE",field_6 = 0,field_7 = 10,
                                     field_8 = "1",field_9 = "500",field_10 = "100",
                                     field_11 = "100",field_12 = null,
                                     field_13 = "ecrlrlep_facilito",
                                     field_14 = "ecrlrlep_facilito",field_15 = "true",
                                     field_16 = "[{codigo_producto, \"0010701020\"}, {tipo_trx_pago, \"10120\"}, {tipo_trx_consulta, \"310120\"}, {payment_type, \"electronic_money\"}]"}]

【讨论】：