add new fields to csv file using powershell

$z = Import-Csv zerotrac.csv
$nums= Import-Csv allleetcode.csv
$md=@{}
#converting one csv into hashmap for quicker search
foreach($r in $nums){
    $md.add($r.frontendQuestionId,$r)
}

foreach($r in $z){
    $nr=$md[$r.id]
    if ($nr){
     $r | Add-Member -MemberType NoteProperty -Name "isPaidOnly" -Value $nr.isPaidOnly
     $r | Add-Member -MemberType NoteProperty -Name "difficulty" -Value $nr.difficulty
     $r | Add-Member -MemberType NoteProperty -Name "topicTags" -Value $nr.topicTags

}

}


$z | Export-Csv -Path "C:\temp\newzerotrac1.csv" -NoTypeInformation

powershell compare two csv files and output differences

 I had to compare data returned from two APIs - one JSON another XML so

1. I used this  viewer to convert json to csv and this app to save xml to csv

2. I used this PowerShell to show difference between two csv files:

Start-Transcript -Path result-10.csv


$mas = Import-Csv 1.csv
$marko = Import-Csv 2.csv

$md=@{}
#converting one csv into hashmap for quicker search
foreach($r in $mas){
    foreach($a in $r.psobject.properties){
        $fn=$a.name
        $val=$a.value
        $md.Add($fn.ToLower(),$val)
    }
}

echo "fieldName,csv1,csv2"

    foreach($r in $marko){
        foreach($a in $r.psobject.properties){

            $k=$a.name.replace("_","").toLower()
            if ($md.ContainsKey($k)){
                if ($md[$k] -ne $a.value){
                  echo "$($a.name),$($a.value),$($md[$k])"
                }
            }
        }
    }
Stop-Transcript

IDataReader into csv

        
        /// <summary>
        ///  Method for converting reader into CSV
        /// </summary>
        /// <param name="dataReader"></param>
        /// <param name="includeHeaderAsFirstRow"></param>
        /// <param name="separator"></param>
        /// <returns></returns>
        public  Stream ToCSV(IDataReader dataReader, bool includeHeaderAsFirstRow, string separator)
        {
            Stream csv = new TempFileStream();
            StreamWriter csvRows = new StreamWriter(csv);
            StringBuilder sb = null;

            if (includeHeaderAsFirstRow)
            {
                sb = new StringBuilder();
                for (int index = 0; index < dataReader.FieldCount; index++)
                {
                    if (dataReader.GetName(index) != null)
                        sb.Append(dataReader.GetName(index));

                    if (index < dataReader.FieldCount - 1)
                        sb.Append(separator);
                }
                csvRows.WriteLine(sb.ToString());
            }

            while (dataReader.Read())
            {
                sb = new StringBuilder();
                for (int index = 0; index < dataReader.FieldCount - 1; index++)
                {
                    if (!dataReader.IsDBNull(index))
                    {
                        string value = dataReader.GetValue(index).ToString();
                        if (dataReader.GetFieldType(index) == typeof(String))
                        {
                            //If double quotes are used in value, ensure each are replaced but 2.
                            if (value.IndexOf("\"") >= 0)
                                value = value.Replace("\"", "\"\"");

                            //If separtor are is in value, ensure it is put in double quotes.
                            if (value.IndexOf(separator) >= 0)
                                value = "\"" + value + "\"";
                        }
                        sb.Append(value);
                    }

                    if (index < dataReader.FieldCount - 1)
                        sb.Append(separator);
                }

                if (!dataReader.IsDBNull(dataReader.FieldCount - 1))
                    sb.Append(dataReader.GetValue(dataReader.FieldCount - 1).ToString().Replace(separator, " "));

                csvRows.WriteLine(sb.ToString());
            }

            csvRows.Flush();
            dataReader.Close();
            return csv;
        }