Styjun

I am trying to complete a problem that pulls from two data sets that need to be combined into one data set. To get to this point, I need to rbind both data sets by the year-month information. Unfortunately, the first data set needs to be tallied by year-month info, and I can't seem to figure out how to change the date so I can have month-year info rather than month-day-year info.
This is data on avalanches and I need to write code totally the number of avalanches each moth for the Snow Season, defined as Dec-Mar. How do I do that?

I keep trying to convert the format of the date to month-year but after I change it with

as.Date(avalancheslc$Date, format="%y-%m")

all the values for Date turn to NA's....help!

# write the webscraper
library(XML)
library(RCurl)
avalanche<-data.frame()
avalanche.url<-"https://utahavalanchecenter.org/observations?page="
all.pages<-0:202
for(page in all.pages)
 this.url<-paste(avalanche.url, page, sep=" ")
 this.webpage<-htmlParse(getURL(this.url))
 thispage.avalanche<-readHTMLTable(this.webpage, which=1, header=T)
 avalanche<-rbind(avalanche,thispage.avalanche)


# subset the data to the Salt Lake Region
avalancheslc<-subset(avalanche, Region=="Salt Lake")
str(avalancheslc)
avalancheslc$monthyear<-format(as.Date(avalancheslc$Date),"%Y-%m")

# How can I tally the number of avalanches?

The final output of my dataset should be something like:

date avalanches
2000-1 18
2000-2 4
2000-3 10
2000-12 12
2001-1 52

This should work (I tried it on only 1 page, not all 203). Note the use of the option stringsAsFactors = F in the readHTMLTable function, and the need to add names because 1 column does not automatically get one.

library(XML)
library(RCurl)
library(dplyr)
avalanche <- data.frame()
avalanche.url <- "https://utahavalanchecenter.org/observations?page="
all.pages <- 0:202
for(page in all.pages)
 this.url <- paste(avalanche.url, page, sep=" ")
 this.webpage <- htmlParse(getURL(this.url))
 thispage.avalanche <- readHTMLTable(this.webpage, which = 1, header = T,
 stringsAsFactors = F)
 names(thispage.avalanche) <- c('Date','Region','Location','Observer')
 avalanche <- rbind(avalanche,thispage.avalanche)


avalancheslc <- subset(avalanche, Region == "Salt Lake")
str(avalancheslc)
avalancheslc <- mutate(avalancheslc, Date = as.Date(Date, format = "%m/%d/%Y"),
 monthyear = paste(year(Date), month(Date), sep = "-"))