@Chris X , Welcome to Microsoft Q&A, based on my research, I find that there is no direct way to give the value like you mentioned.
We could only use loop to do it. Maybe the following code will be more simpler.
var list = df["Dates"].Cast<DateTime>().Select(i => i.Ticks).ToList();
for (int i = 0; i < list.Count; i++)
{
df["Ticks"][i] = list[i];
}
Hope this could help you.
Best Regards,
Jack
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