按条件选择行
、 =、%in%、!...[max(number),]
d e c name money number
1: 2 1 expensive orange 6 6
选择或删除某列
对列进行计算..., by = c("name"))
[1] 3
key(dt, colname)设置索引
setkey(dt, NULL) 去除索引
⚠️:当提取的索引是数字时格式不同
> setkey(dt, name...读取或写出文件
fread(".csv", select = c("a","b")) 读取.csv或.tsv格式的文件,可以选择特定列读取
fwrite(dt, ".csv")...foverlaps(x, y, type="any", mult="first")
⚠️:如果x和y索引的列名称不同时,在foverlaps()内加上一行参数
by.x =c("", "", "")