Compare dates with different formats in csv file

问题

Whats a good way to compare dates in a csv file that looks like this:

Date1,Date2,Date3
11/10/2016  9:45:00 PM,20161110,11/10/2016
11/15/2016  11:24:00 PM,20160924,11/10/2016

If a match is found, append a column like so...

Date1,Date2,Date3,MatchDates
11/10/2016  9:45:00 PM,20161110,11/10/2016,Match Found
11/15/2016  11:24:00 PM,20160924,11/10/2016,No Match Found

updated

Trying the code that is in the comments:

When comparing this with 2 of the columns...

$csvFile = 'C:\Scripts\Tests\test1.csv'

Import-Csv $csvFile | Select-Object *, @{n='MatchDates';e={
if(([datetime]$_.Date1).Date -eq $_.Date3){
'Match Found'
}Else{
'No Match Found'
}}} | 
    Export-Csv "$csvFile-results.csv" -NoTypeInformation -Force

output (isCorrect)...

Date1,Date2,Date3,MatchDates
11/10/2016  9:45:00 PM,20161110,11/10/2016,Match Found
11/15/2016  11:24:00 PM,20160924,11/10/2016,No Match Found

However, if I try to compare all 3 columns using the following code

Import-Csv $csvFile | Select-Object *, @{n='MatchDates';e={
if((([datetime]$_.Date1).Date -eq $_.Date3) -and (([datetime]$_.Date2).Date -eq $_.Date3) -and (([datetime]$_.Date1).Date -eq $_.Date2)){
'Match Found'
}Else{
'No Match Found'
}}} | 
    Export-Csv "$csvFile-results.csv" -NoTypeInformation -Force

output (isNotCorrect)...

Date1,Date2,Date3,MatchDates
11/10/2016  9:45:00 PM,20161110,11/10/2016,
11/15/2016  11:24:00 PM,20160924,11/10/2016,No Match Found

As you can see the value of row 1 and the last column is $null instead of showing Match Found

Maybe I'm not understanding something correctly?

回答1:

You were on the right track with what we discussed in comments. Problem was with that middle date. It does not convert to a [datetime] without some help. That is where ParseExact comes in handy. Consider the following:

PS D:\temp> [datetime]"20160924"
Cannot convert value "20160924" to type "System.DateTime". Error: "String was not recognized as a valid DateTime."
At line:1 char:1
+ [datetime]"20160924"
+ ~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidArgument: (:) [], RuntimeException
    + FullyQualifiedErrorId : InvalidCastParseTargetInvocationWithFormatProvider


PS D:\temp> [datetime]::parseexact("20160924","yyyyMMdd",[System.Globalization.CultureInfo]::CurrentCulture)

Saturday, September 24, 2016 12:00:00 AM

Note the second example returned a proper date object.

---

Do you remember the transitive property from math? We use that for simple comparison to see if all dates are the same. Not the only way by far but a simple one nonetheless. Building off your calculated property code

$csv |  Select-Object *,@{Name='MatchDates';Expression={
        $date1 = ([datetime]$_.Date1).Date
        $date2 = ([datetime]::parseexact($_.Date2,"yyyyMMdd",[System.Globalization.CultureInfo]::CurrentCulture)).Date
        $date3 = ([datetime]$_.Date1).Date
        if($date1 -eq $date2 -and $date2 -eq $date3){
            'Match Found'
        } else {
            'No Match Found'
        }
    }
}

Cleared up the if logic by saving the casted values in temproary variables.

来源：https://stackoverflow.com/questions/34423960/compare-dates-with-different-formats-in-csv-file