如何仅将满足条件的行从csv读取到R中? [英] How to read only lines that fulfil a condition from a csv into R?

问题描述

我正在尝试将大型csv文件读取到R中.我只想读取并使用满足特定条件的某些行(例如Variable2 >= 3).这是一个非常小的数据集.

I am trying to read a large csv file into R. I only want to read and work with some of the rows that fulfil a particular condition (e.g. Variable2 >= 3). This is a much smaller dataset.

我想直接将这些行读取到数据框中，而不是将整个数据集加载到数据框中，然后根据条件进行选择，因为整个数据集不容易装入内存中.

I want to read these lines directly into a dataframe, rather than load the whole dataset into a dataframe and then select according to the condition, since the whole dataset does not easily fit into memory.

推荐答案

您可以在sqldf包中使用read.csv.sql函数，并使用SQL select进行过滤.从read.csv.sql的帮助页面:

You could use the read.csv.sql function in the sqldf package and filter using SQL select. From the help page of read.csv.sql:

library(sqldf)
write.csv(iris, "iris.csv", quote = FALSE, row.names = FALSE)
iris2 <- read.csv.sql("iris.csv", 
    sql = "select * from file where `Sepal.Length` > 5", eol = "\n")

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