Julia DataFrames.jl-使用NA过滤数据(NAException) [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)

我可以在列:a

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

但是如果我在:b上尝试相同的操作，则会收到错误NAException("cannot index an array with a DataArray containing 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.

我的问题是通常应如何处理带有NA的DataFrame?我可以理解，针对NA的>或<操作将为undefined，但==应该可以工作(否?).

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

您在此处的期望行为是什么?如果要进行这样的选择，则可以使条件(不是NAN)为AND(等于4).如果第一个测试失败，则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]),:]

这篇关于Julia DataFrames.jl-使用NA过滤数据(NAException)的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！