Julia DataFrames.jl - 使用 NA (NAException) 过滤数据 [英] Julia DataFrames.jl - filter data with NA's (NAException)

问题描述

我不确定如何在 Julia DataFrames 中处理 NA.

I am not sure how to handle NA within Julia DataFrames.

例如使用以下 DataFrame:

For example with the following DataFrame:

> import DataFrames
> a = DataFrames.@data([1, 2, 3, 4, 5]);
> b = DataFrames.@data([3, 4, 5, 6, NA]);
> ndf = DataFrames.DataFrame(a=a, b=b)

我可以成功对列:a

> ndf[ndf[:a] .== 4, :]

但如果我在 :b 上尝试相同的操作，我会收到错误 NAException("cannot index an array with a DataArray contains NA values").

but if I try the same operation on :b I get an error NAException("cannot index an array with a DataArray containing NA values").

> ndf[ndf[:b] .== 4, :]

NAException("cannot index an array with a DataArray containing NA values")
while loading In[108], in expression starting on line 1

in to_index at /Users/abisen/.julia/v0.3/DataArrays/src/indexing.jl:85
in getindex at /Users/abisen/.julia/v0.3/DataArrays/src/indexing.jl:210
in getindex at /Users/abisen/.julia/v0.3/DataFrames/src/dataframe/dataframe.jl:268

这是因为存在 NA 值.

Which is because of the presence of NA value.

我的问题是通常应该如何处理带有 NA 的 DataFrames?我可以理解 > 或 < 对 NA 的操作将是 undefined 但 == 应该可以工作(不是吗?).

My question is how should DataFrames with NA should typically be handled? I can understand that > or < operation against NA would be undefined but == should work (no?).

推荐答案

你想要的行为是什么?如果您想做这样的选择，您可以设置条件(不是 NAN)AND(等于 4).如果第一个测试失败，那么第二个测试永远不会发生.

What's your desired behavior here? If you want to do selections like this you can make the condition (not a NAN) AND (equal to 4). If the first test fails then the second one never happens.

using DataFrames
a = @data([1, 2, 3, 4, 5]);
b = @data([3, 4, 5, 6, NA]);
ndf = DataFrame(a=a, b=b)
ndf[(!isna(ndf[:b]))&(ndf[:b].==4),:]

在某些情况下，您可能只想删除某些列中带有 NA 的所有行

In some cases you might just want to drop all rows with NAs in certain columns

ndf = ndf[!isna(ndf[:b]),:]

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