Histogram of Weekdays by Year R - r

Question

I have a .csv file that I have loaded into R using the following basic command:
lace <- read.csv("lace for R.csv")
It pulls in my data just fine. Here is the str of the data:
str(lace)
'data.frame': 2054 obs. of 20 variables:
$ Admission.Day : Factor w/ 872 levels "1/1/2013","1/10/2011",..: 231 238 238 50 59 64 64 64 67 67 ...
$ Year : int 2010 2010 2010 2011 2011 2011 2011 2011 2011 2011 ...
$ Month : int 12 12 12 1 1 1 1 1 1 1 ...
$ Day : int 28 30 30 3 4 6 6 6 7 7 ...
$ DayOfWeekNumber : int 3 5 5 2 3 5 5 5 6 6 ...
$ Day.of.Week : Factor w/ 7 levels "Friday","Monday",..: 6 5 5 2 6 5 5 5 1 1 ...
What I am trying to do is create three (3) different histograms and then plot them all together on one. I want to create a histogram for each year, where the x axis or labels will be the days of the week starting with Sunday and ending on Saturday.
Firstly how would I go about creating a histogram out of Factors, which the days of the week are in?
Secondly how do I create a histogram for the days of the week for a given year?
I have tried using the following post here but cannot get it working. I use the Admission.Day as the variable and get an error message:
dat <- as.Date(lace$Admission.Day)
Error in charToDate(x) : character string is not in a standard unambiguous format
Thank you,

Answer 1

Expanding on the comment above: the problem seems to be with importing dates, rather than making the histogram. Assuming there is an excel workbook "lace for R.xlsx", with a sheet "lace":
## Not tested...
library(XLConnect)
myData <- "lace for R.xlsx" # NOTE: need path also...
wb <- loadWorkbook(myData)
lace <- readWorksheet(wb, sheet="lace")
lace$Admission.Day <- as.Date(lace$Admission.Day)
should provide dates that work with all the R date functions. Also, the lubridate package provides a number of functions that are more intuitive to use than format(...).
Then, as an example:
library(lubridate) # for year(...) and wday(...)
library(ggplot2)
# random dates around Jun 1, across 5 years...
set.seed(123)
lace <- data.frame(date=as.Date(rnorm(1000,sd=50)+365*(0:4),origin="2008/6/1"))
lace$year <- factor(year(lace$date))
lace$dow <- wday(lace$date, label=T)
# This creates the histograms...
ggplot(lace) +
geom_histogram(aes(x=dow, fill=year)) + # fill color by year
facet_grid(~year) + # facet by year
theme(axis.text.x=element_text(angle=90)) # to rotate weekday names...
Produces this: