# 函数目标:

# 读取文件中的指定行和指定列

# 不包括注释行

read_part <- function(file, rows = 1, columns = -1, sep = "\t",

stringsAsFactors = FALSE,

header = FALSE,

check.names = FALSE,

comment.char = "#", ...){

dfl <- list()

if (grepl("gz$", file)){

con <- gzfile(file, open = "rb")

} else{

con <- file(file, open = "r")

}

i <- 0

j <- 1

repeat{

rec <- readLines(con, 1)

if (length(rec) == 0) break

i <- i + 1

# 当rows = -1时, 会读取所有行

# 超过目标行时停止读取

if (i > max(rows) & rows != -1) break

# 不考虑注释行

if (grepl(comment.char, rec )) next

if ( ! i %in% rows & rows != -1) next

items <- strsplit(rec, split = sep, fixed = TRUE)[[1]]

if ( columns == -1){

select_cols <- items

} else{

select_cols <- items[columns]

}

#print(select_cols)

dfl[[j]] <- select_cols

j <- j + 1

}

close(con)

df <- do.call(rbind, dfl)

return(df)

}