帮我用“应用"替换 for 循环功能 [英] Help me replace a for loop with an "apply" function

问题描述

...如果可以的话

我的任务是找出用户参与游戏的最长连续天数.

My task is to find the longest streak of continuous days a user participated in a game.

我没有编写 sql 函数，而是选择使用 R 的 rle 函数，以获得最长的连续记录，然后用结果更新我的数据库表.

Instead of writing an sql function, I chose to use the R's rle function, to get the longest streaks and then update my db table with the results.

(附加的)数据框是这样的:

The (attached) dataframe is something like this:

    day      user_id
2008/11/01    2001
2008/11/01    2002
2008/11/01    2003
2008/11/01    2004
2008/11/01    2005
2008/11/02    2001
2008/11/02    2005
2008/11/03    2001
2008/11/03    2003
2008/11/03    2004
2008/11/03    2005
2008/11/04    2001
2008/11/04    2003
2008/11/04    2004
2008/11/04    2005

我尝试了以下方法来获得每个用户最长的连续记录

I tried the following to get per user longest streak

# turn it to a contingency table
my_table <- table(user_id, day)

# get the streaks
rle_table <- apply(my_table,1,rle)

# verify the longest streak of "1"s for user 2001
# as.vector(tapply(rle_table$'2001'$lengths, rle_table$'2001'$values, max)["1"])

# loop to get the results
# initiate results matrix
res<-matrix(nrow=dim(my_table)[1], ncol=2)

for (i in 1:dim(my_table)[1]) {
string <- paste("as.vector(tapply(rle_table$'", rownames(my_table)[i], "'$lengths, rle_table$'", rownames(my_table)[i], "'$values, max)['1'])", sep="")
res[i,]<-c(as.integer(rownames(my_table)[i]) , eval(parse(text=string)))
}

不幸的是，这个 for 循环花费的时间太长，我想知道是否有办法使用apply"系列中的函数生成 res 矩阵.

Unfortunately this for loop takes too long and I' wondering if there is a way to produce the res matrix using a function from the "apply" family.

先谢谢你

推荐答案

另一个选项

# convert to Date
day_table$day <- as.Date(day_table$day, format="%Y/%m/%d")
# split by user and then look for contiguous days
contig <- sapply(split(day_table$day, day_table$user_id), function(.days){
    .diff <- cumsum(c(TRUE, diff(.days) != 1))
    max(table(.diff))
})

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