Cannot find an overload for "ToString" and the argument count: "1"

Question

i'm not understanding what i'm doing wrong here since i seem to do the same thing but only one works.

i have a text file with a number list that i want to process (round the values):

39.145049
40.258140
41.400803
42.540093
43.664530

and here my script:

$a = get-content "input.txt"
$b = $a -join ','
$b | % {$_.ToString("#.###")}

this results in the following error:

Cannot find an overload for "ToString" and the argument count: "1".
At D:\script.ps1:9 char:9
+ $b | % {$_.ToString("#.###")}
+         ~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [], MethodException
    + FullyQualifiedErrorId : MethodCountCouldNotFindBest

however if i take the result after joining which is:

39.145049,40.258140,41.400803,42.540093,43.664530

and create the following script:

$b = 39.145049,40.258140,41.400803,42.540093,43.664530
$b | % {$_.ToString("#.###")}

it works just fine and outputs:

39.145
40.258
41.401
42.54
43.665

where am i going wrong on this one?

Answer 1

发生这种情况的原因是输入的类型不同。

$b1 = $a -join ','
$b2 = 39.145049,40.258140,....

$b1.GetType().Name
String

$b2.GetType().Name
Object[]

由于第一种情况下的输入是单个字符串，因此foreach循环不会将其处理为十进制值的集合，而是一个字符串。因此，

$b | % {$_.ToString("#.###")}

要做（作为伪代码）：

'39.145049,40.258140,41.400803,42.540093,43.664530'.ToString("#.###")

数组版本正在做

39.145049.ToString("#.###")
40.258140.ToString("#.###")
41.400803.ToString("#.###")

Powershell能够在以后的情况中确定这些值是数字。在第一种情况下，它只是一个字符串，因此自动转换不起作用。

在第一种情况下实际起作用的是将值强制转换为数字。像这样

$a | % {$([double]$_).ToString("#.###")}
39,145
40,258
41,401
42,54
43,665