Dears hope you can help,
i am try to convert date time to date i used the below 
#to convert date time to date
EcommerceDate <- ECommerce %>%
mutate(Date=as.Date(ECommerce$InvoiceDate, format = "%m/%d/%Y %I:%M"))
create Month year date
EcommerceMonthYear <- EcommerceDate %>%
mutate(Month_Year=strftime(Ecommerce2$Date,format="%Y/%m"))
XXX <- Ecommerce_Clean2 %>% group_by(Month_Year) %>% summarise(count=n())
XXX
A tibble: 16 x 2
Month_Year count
1 0201/10 43920
2 0201/11 61632
3 0201/12 19464
4 2010/12 22016
5 2011/01 34306
6 2011/02 27105
7 2011/03 35803
8 2011/04 29096
9 2011/05 36164
10 2011/06 35977
11 2011/07 38645
12 2011/08 34483
13 2011/09 49261
14 2011/10 15384
15 2011/11 21737
16 2011/12 25111
I am getting "0201" in the year part, however there is no "0201" in my invoicedate field.
Please advice