R中的陈述

Question

对于某个项目，我有一个脚本，它从csv文件中获取日期：

reviewFile = "csvfile"
reviews = read.csv(reviewFile, stringsAsFactors=FALSE, sep = '\t')
names(reviews) <- c("date","rating","helpful","total","title","text")

reviews$date <- as.Date(reviews$date, "%Y-%m-%d") 
reviews$month <- as.Date(cut(reviews$date, breaks = "month"))

aggr <- aggregate(reviews$rating ~ reviews$month, FUN = mean) 
aggr$freq = count(reviews$month)$freq 
names(aggr) <- c("month","avg_rating","num_ratings") 

par(mfrow=c(2,1))

plot(aggr$month, aggr$num_ratings, type="s", xlab="Month", ylab="# ratings")

如您所见，这需要一个csv文件并将其绘制成图形。 我如何在这里实现for()循环，以便仅从2010（或2010-01）开始进行评论，例如在图中实现？

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以下是数据输入的示例。 它们都有相同的构造。 我是R的新手，是否必须在date变量中添加if语句？

2003-09-30  5.0 1   2   2-Fast-2-Furious-(Widescreen-Edition)   THIS MOVIE KEEPS U ON THE EDGE OF U'R SEAT BUT AT THE SAME TIME MAKES U LAUGH.. I CAN'T C Y PEEP'S DITCH THIS MOVIE OR THE FIRST UNLESS THEY WERE BORN UNDER A ROCK.... PAUL WALKER RETURNS & DOES AN X-CELENT JOB ... TYRESE A NEW UPCOMING STAR ALSO PROVIDES AN X-CELENT JOB AS HIS CO-PARTNER 

Answer 1

# build some example data
dat <- data.frame(date= as.Date(12000:12500, origin = "1970-01-01"),
                  val= rnorm(501))
dat$mo <- as.Date(cut(dat$date, breaks= "month"))

# use OP's aggregation on ex data
aggr <- aggregate(dat$val ~ dat$mo, FUN = mean) 
aggr$freq = as.integer(table(dat$mo))
names(aggr) <- c("month","avg_rating","num_ratings") 

par(mfrow= c(1,2))
# base plot
plot(num_ratings ~ month, data= aggr, 
     type="s", xlab="Month", ylab="# ratings")

# subset based on date
plot(num_ratings ~ month, data= aggr[aggr$month >= as.Date("2003-01-01", format= "%Y-%m-%d"),], 
     type="s", xlab="Month", ylab="# ratings")

左：原始图，右：子集图