Scrape Historical NHL Skaters Data

nhl_skaters.R

# LOAD LIBRARIES REQUIRED

library(plyr);
library(XML)

# FIGURE OUT PATTERN OF URL FOR EACH SEASON

url.b1 = 'http://ca.sports.yahoo.com/nhl/stats/byposition?pos=C,RW,LW,D';
url.b2 = '&sort=14&conference=NHL&year=season_';
url.b3 = y;

# WRITE FUNCTION TO EXTRACT DATA FOR A SEASON

extract_data = function(y){
	
	url    = paste(url.b1, url.b2, as.character(y), sep = '');
	tab    = readHTMLTable(url, stringsAsFactors = F)[[4]];
	tab    = tab[,-c(2*(2:16))] # remove empty columns
	names(tab) = tab[1,];
	tab		   = tab[-1,];
	tab$year   = y;
	tab
}

# APPLY FUNCTION TO EXTRACT DATA FOR ALL SEASONS

skaters = ldply(2005:2010, extract_data, .progress = 'text');

# CLEAN DATA FRAME AS REQUIRED

skaters[,-c(1, 2)] = sapply(skaters[, -c(1, 2)], as.numeric);
skaters[, c(1, 2)] = sapply(skaters[, c(1, 2)], as.factor);
names(skaters) = tolower(names(skaters));
names(skaters)[7] = 'pm'

write.csv(skaters, 'skaters.csv', row.names = F);

I meet this error in R '错误于class(output[[var]]) <- class(value) : NULL是不能有属性的', I make y equal to 2012 and have ldply(2009:2012, extract_data, .progress = 'text'). Could explain to why i meet this problem? Than you so much.