在 POSIXct 的向量上使用 sapply [英] Using sapply on vector of POSIXct

问题描述

我有一个可能非常简单的问题.我想从数据帧处理一列 POSIXct 对象并生成一个日期时间字符串向量.我尝试使用以下 sapply 调用

I have what may be a very simple question. I want to process a column of POSIXct objects from a dataframe and generate a vector of datetime strings. I tried to use the following sapply call

dt <- sapply(df$datetime, function(x) format(x,"%Y-%m-%dT%H:%M:%S"))

但无济于事.我不断收到以下错误:

but to no avail. I keep getting the following error:

> Error in prettyNum(.Internal(format(x, trim, digits, nsmall, width, 3L,  :
invalid 'trim' argument

当我将此函数应用于列中的单个 POSIXct 对象时，我没有问题.所以我现在对问题所在感到困惑.我需要对 POSIXct 对象做一些特别的事情吗?

When I apply this function to a single POSIXct object from the column, I have no problem. So I'm stumped at the moment about what the problem is. Do I need to do something special with POSIXct objects?

推荐答案

format() 将采用向量参数，所以format(df$datetime,"%Y-%m-%dT%H:%M:%S") 应该可以满足您的需求.

format() will take a vector argument, so format(df$datetime,"%Y-%m-%dT%H:%M:%S") should do what you need.

当您使用 sapply 时，您的对象被强制转换为数字，因此调用了错误的格式方法.您可以使用 sapply(df$datetime, function(x) format(as.POSIXct(x, origin="1970-01-01"),"%Y-%m-%dT) 将它们强制回 POSIXct%H:%M:%S"))，但是除非你有特殊的理由使用apply，就用上面的方法

When you use sapply, your objects are coerced to numeric, and so the wrong format method is being invoked. You could coerce them back to POSIXct by using sapply(df$datetime, function(x) format(as.POSIXct(x, origin="1970-01-01"),"%Y-%m-%dT%H:%M:%S")), but unless you have a special reason to use apply, just use the method above

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