从无值的Python INT列表初始化numpy的屏蔽数组 [英] Initializing numpy masked array from Python int list with None values

问题描述

如图中问题的答案<一href=\"http://stackoverflow.com/questions/19456239/convert-python-list-with-none-values-to-numpy-array-with-nan-values\">Convert与无值蟒蛇名单numpy的阵列NaN值，它是直接从具有无值的列表初始化一个蒙面numpy的数组，如果我们执行DTYPE =浮动。这些浮点值被转换为NaN，我们可以简单地做：

As shown in the answer to the question Convert python list with None values to numpy array with nan values, it is straightforward to initialize a masked numpy array from a list with None values if we enforce the dtype=float. Those float values get converted to nan and we can simply do:

ma.masked_invalid(np.array(a, dtype=float), copy=False)

这不过不会像INT工作：

This however will not work for int like:

ma.masked_invalid(np.array(a, dtype=int), copy=False)

由于中间np.array不会与没有值被创建（没有INT南）。

since the intermediate np.array will not be created with None values (there is no int nan).

什么是初始化基于整数的Python列表上一个蒙面的数组，也包含这样的方式，那些无值变为屏蔽无值的最有效方法是什么？

What is the most efficient way to initialize a masked array based on Python list of ints that also contains None values in such way that those None values become masked?

推荐答案

最优雅的解决方案到目前为止，我已经找到（它是不优雅可言）是初始化类型的屏蔽数组浮动，并将其转换为 INT 算账：

The most elegant solution I have found so far (and it is not elegant at all) is to initialize a masked array of type float and convert it to int afterwards:

ma.masked_invalid(np.array(a, dtype=float), copy=False).astype(int)

这会产生一个适当的NP阵列初始阵列在无值 A 被屏蔽。例如，对于

This generates a proper NP array where None values in the initial array a are masked. For instance, for:

a = [1, 2, 3, None, 4]
ma.masked_invalid(np.array(a, dtype=float), copy=False).astype(int)

我们得到：

masked_array(data = [1 2 3 -- 4],
             mask = [False False False  True False],
       fill_value = 999999)

另外，实际蒙面INT值变得分钟INT，即

Also, the actual masked int values become min int, i.e.

ma.masked_invalid(np.array(column, dtype=float), copy=False).astype(int).data

给出了：

array([                   1,                    2,                    3,
       -9223372036854775808,                    4])

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