从Web导入Mathematica中的表 - 空单元格问题 [英] Importing tables in Mathematica from web - empty cell problem
问题描述
我使用：
data = Import [http：// weburl /，Data]
从一个站点导入数据。在该页面上有表格。这将创建嵌套列表，您可以轻松地以表格形式获取数据。例如：
Grid [data [[1]]]
会给出这样的结果：
I use:
data=Import["http://weburl/","Data"]
to import data from one site. On that page there are tables. This creates nested lists, and you can easily get the data in table form. For example:
Grid[data[[1]]]
would give something like this:
Player Age Shots Goals
P1 24 10 2
P2 22 5 0
P3 28 11 1
...
现在，问题出在这里。如果html表中的一个单元格为空，例如Age的条目，那么在html中，这将是这样的：< td>< / td> 。 Mathematica根本不包括它在列表中，甚至不包括，例如，Null值。相反，这一行只是由长度为3的列表表示，数据将被移动一列，因此您将获得镜头代替年龄和目标代替镜头和目标 会空的。
例如，一个年龄未知的P4（html表格中的空单元格），有10个镜头并且得分为0的目标将被导入长度为3而不是4的列表并移动一个：
Now, here is the problem. If one cell in the html table is empty, for example an entry for "Age", then in html this would look like this: <td></td>. Mathematica doesn't include take it in the list at all, not even as, for example, a "Null" value. Instead, this row would just be represented by a list of length 3 and data would be moved by one column, so you'd get "Shots" in place of "Age" and "Goals" in place of "Shots" and "Goals" would be empty.
For example, a "P4" whos age is unknown (empty cell in html table), who had 10 shots and scored 0 goals would be imported as list of length 3 not 4 and moved by one:
Player Age Shots Goals
P1 24 10 2
P2 22 5 0
P3 10 0
...
这会带来一个难题，因为如果你有一些空字段那么你无法从列表中分辨出它属于哪一列。在Mathematica中导入时，有没有办法在html表中的空单元格上放置Null？例如，列表中的P4元素如下所示：
data [[1,5]]
{P4，Null，10,0}
而不是：
{P4 ，10,0}
This poses a difficult problem, because if you have a few empty fields then you can't tell from the list to which column it belongs. Is there a way to put a "Null" on an empty cell in html tables when importing in Mathematica? For example, P4 element in list would look like this:
data[[1,5]]
{"P4","Null",10,0}
instead of:
{"P4",10,0}
推荐答案
正如lumeng指出的那样，你可以使用 FullData 以使HTML表格元素正确填写。以下是对此的简单说明。
As lumeng points out, you can use FullData to get the HTML table element to fill out properly. Here's a simpler illustration of this.
in = ImportString["\<<html><table>
<tr>
<td>(1,1)</td>
<td>(1,2)</td>
<td>(1,3)</td>
</tr>
<tr>
<td>(2,1)</td>
<td></td>
<td>(2,3)</td>
</tr>
</table></html>\>",
{"HTML", "FullData"}];
Grid[in[[1, 1]]]
如果你想要更完整的控制输出，我建议你导入页面为XML。这是一个例子。
If you want more complete control of the output, I'd suggest that you Import the page as XML. Here's an example.
in = ImportString["\<<html><table>
<tr>
<td>(1,1)</td>
<td>(1,2)</td>
<td>(1,3)</td>
</tr>
<tr>
<td>(2,1)</td>
<td></td>
<td>(2,3)</td>
</tr>
</table></html>\>", "XML"];
Column[Last /@ Cases[in,
XMLElement["td", ___], Infinity]]
您需要阅读一般的XML和Mathematica的版本，即 XMLObject 。不过，一旦你掌握了它，这是一种乐趣。
You'll need to read up a bit on XML in general and Mathematica's version, namely the XMLObject. It's a delight to work with, once you get the hang of it, though.
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