两个减号的含义（“双一元”） [英] Meaning of two minus signs together ("double unary")

问题描述

例如：
此公式获取字符串日期并将其转换为Excel日期序列号：

  =  - （MID（S2,4 ，3）& LEFT（S2,3）&MID（S2,7,4））
  

公式工作正常，我只想了解公式中的 - 。

解决方案

@ JNevill的评论对我来说似乎是一个很好的答案，但为了答案考虑在A1和 Y Y c $ c>在B1。这个公式：

  =（A1 = B1）
  

返回TRUE。如前所述，将操作符放在前面（ 0 + 或 1 * ），并将布尔值变为 1 或 0 如果B1（仅）更改为，例如 X 。

单数减去否定。 0 - 或 -1 * ，在前面返回 -1 A1和B1等于 Y 。 和 -1 结果变为 1 ，与 = - 1 *（A1 = B1）。

但是乘以1（或添加零）是无意义的，可能只是去：

  =  - （A1 = B1）
  

请注意，因为评估发生的顺序，上述方法与以下不同：

  =  -  A1 = B1 
  

没有意义，所以返回 #VALUE！。 / p>

您的示例中的文本函数（ MID 和 LEFT 返回字符串，因此，使用这样的函数（单独）构建今天的日期索引（在1900日期系统中为42311）返回Excel不能识别为可能表示日期的五个字符。转换为数字格式并表示为日期，这应该是今天。

所以格式化为单元格作为文本并输入42311，然后重新格式化为日期，结果仍然是$ code> 42311 。将单元格格式化为常规，然后输入：

  =  - （42&311）
  

然后格式化为日期，您应该看到一些看起来像今天的东西。

What does the two - sign mean at the beginning of a formula?

Ex: This formula gets a string date and converts it into an Excel date serial number:

=--(MID(S2,4,3)&LEFT(S2,3)&MID(S2,7,4))

The formula works fine, I just want to understand the -- in the formula.

解决方案

@JNevill's Comment seems a good answer to me but for the sake of an Answer consider Y in A1 and Y in B1. This formula:

=(A1=B1)  

returns TRUE. As mentioned, stick an operator in front (with 0+, or 1*) and the Boolean is turned into 1, or 0 if B1 (only) is changed to, say, X.

The single minus negates that. 0-, or -1*, at the front returns -1 for both A1 and B1 equal to Y. Negate that and the -1 result becomes 1, say with =--1*(A1=B1).

But then multiplying by one (or adding zero) is pointless, might as well just go for:

=--(A1=B1)  

Note that because of the order in which the evaluations take place, the above is not the same as:

=--A1=B1  

which has no meaning so returns #VALUE!.

Text functions (MID and LEFT in your example) return strings, so constructing a date index for today for example (42311 in the 1900 date system) with such functions (alone) returns five characters Excel does not recognise as possibly representing a date. Converted to numeric format and represented as a date this should look like 'today'.

So format as cell as Text and enter 42311, then reformat as Date and the result is still 42311. Format a cell as General and enter:

=--("42"&"311")

before then formatting as Date and you should see something that looks like 'today'.

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