Why does this code plot by day of the week? - r

Question

Link to the data set which is a date and time column along with electricity usage columns
https://d396qusza40orc.cloudfront.net/exdata%2Fdata%2Fhousehold_power_consumption.zip
power1 <- read.csv(file = "c:/datasets/household_power_consumption.txt", stringsAsFactors=F, header = TRUE,
sep=";", dec = ".", na.strings="?", col.names = c("date1","time1","Global_active_power", "Global_reactive_power",
"Voltage","Global_intensity","Sub_metering_1","Sub_metering_2",
"Sub_metering_3"))
power1$date1 <- as.Date(power1$date1, format="%d/%m/%Y")
power2 <- subset(power1, subset=(date1 >= "2007-02-01" & date1 <= "2007-02-02"))
datetime1 <- paste(as.Date(power2$date1), power2$time1)
power2$Datetime <- as.POSIXct(datetime1)
plot(power2$Global_active_power~power2$Datetime, type="l", ylab="Global Active Power (kilowatts)", xlab="")
When I run the above, I get the graph like I'm supposed to with the days of the week on the x axis even when I run summary, head and str() I don't see anything in the data about days of the week.
I tried to add my own day column with mutate but it didn't work.
And it didn't work when I subset it like the following. It subset properly where I had only the data I needed, but it wouldn't plot with the date1 column or the day of the week column I created via mutate
power2 <- subset(power1, subset=(as.Date(date1, format = "%d/%m/%Y") >= "2007-02-01"
& as.Date(date1, format = "%d/%m/%Y") <= "2007-02-02"))
I know that as.Posixct will have all the metadata in there, but I don't understand why is it when I combine the date and time columns into it's own column only then it plots by day of the week graphwithout me asking.
When I run it like this, the combined date and time column data is corrupted with the wrong year
power11 <- read.csv(file = "c:/datasets/household_power_consumption.txt", stringsAsFactors=F, header = TRUE,
sep=";", dec = ".", col.names = c("date1","time1","Global_active_power", "Global_reactive_power",
"Voltage","Global_intensity","Sub_metering_1","Sub_metering_2",
"Sub_metering_3"))
#colClasses = c("Date", "character", "factor", "numeric","numeric","numeric","numeric","numeric","numeric"))
power22 <- subset(power11, subset=(as.Date(date1, format = "%d/%m/%Y") >= "2007-02-01"
& as.Date(date1, format = "%d/%m/%Y") <= "2007-02-02"))
datetime1 <- paste(as.Date(power22$date1), power22$time1)
power22$Datetime <- as.POSIXct(datetime1)

Answer 1

Maybe this link would be helpful:
http://earlh.com/blog/2009/07/07/plotting-with-custom-x-axis-labels-in-r-part-5-in-a-series/
add an argument to your plot() call: xaxt='n'
plot(power2$Global_active_power~power2$Datetime, type="l", ylab="Global Active Power (kilowatts)", xlab="", xaxt='n')
that tells plot not to add x-axis labels. Then add an axis() call:
axis(side=1, at=power22$Datetime, labels=format(power22$Datetime, '%b-%y'))
I used '%b-%y' here, because that's what I saw on the site I referenced, but you would want to use the format code appropriate to your needs.