如何按F#中的值按行分组? [英] How to group by values in a row in F#?

问题描述

如果我已上传CSV文件，并且将其拆分为SEQUENCE中的行.

If I have uploaded a CSV file and I have it split up into rows within a SEQUENCE.

如果说ROW 1中也存在一个值的多个实例，如何用ROW 1中的值对ROW 2中的值求平均，所以现在我在ROW 1中只有每个值的一个实例.>{这只是一个例子，ROW 1和ROW 2是理论上的.}

If there are also multiple instances of one value in lets say ROW 1, how do I average the values in ROW 2 by the values in ROW 1, so I now only have one instance of each value in ROW 1.
{This is just an example, and ROW 1 and ROW 2 are theoretical.}

请注意，我正在处理序列.

Be aware that I am working with a sequence.

数据示例和理想结果如下:

Example of data and ideal result is below:

给出了什么:

Row 1 --- Row 2 (Dollars)   
2010  ---    50000.198  
2010  ---    45151.451  
2011  ---    75641.372  
2011  ---    91652.710  
2012  ---    11281.450  
2012  ---    70046.154  
2012  ---    97778.054  
2013  ---    555574.501 
2013  ---    78921.215

我想要什么:

Row 1 --- Row 2
2010  ---    47575.825
2011  ---    93647.041
2012  ---    59701.886 
2013  ---    317247.858

推荐答案

听起来您已经解析了CSV文件并将值拉入序列中.对于此示例，假设您将其拉入元组列表，其中以年为第一个元素，成本为第二个元素，等效于此:

It sounds like you've already parsed the CSV file and pulled values into a sequence. For this example, let's assume you pulled it into a list of tuples with the year as the first element and the cost as the second, equivalent to this:

let costByYear =
    [
    (2010,50000.198)
    (2010,45151.451)
    (2011,75641.372)
    (2011,91652.710)
    (2012,11281.450)
    (2012,70046.154)
    (2012,97778.054)
    (2013,555574.501)
    (2013,78921.215)
    ]

您可以使用一些 Seq 函数按年份分组(

You could use a few Seq functions to group by the year (Seq.groupBy) and then average the cost (Seq.average):

let avgCostPerYear =
    let avg (year, costs) = (year, Seq.average <| Seq.map snd costs)
    Seq.groupBy fst >> Seq.map avg

运行此:

printfn "%A" (avgCostPerYear costByYear)

产量:

seq
  [(2010, 47575.8245); (2011, 83647.041); (2012, 59701.886); (2013, 317247.858)]

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