R：计算组的子集的平均值 [英] R: Calculate means for subset of a group

问题描述

我想计算每个日的平均值，但计算一天的一部分（时间= 12-14）。这段代码适用于我，但我必须输入每一天作为一行新的代码，这将达数百行。

I want to calculate the mean for each "Day" but for a portion of the day (Time=12-14). This code works for me but I have to enter each day as a new line of code, which will amount to hundreds of lines.

这似乎应该很简单。我已经做到这一点很容易当分组变量是相同的，但不知道如何做，当我不想包括一天的所有值。
有更好的方法吗？

This seems like it should be simple to do. I've done this easily when the grouping variables are the same but dont know how to do it when I dont want to include all values for the day. Is there a better way to do this?

sapply(sap[sap$Day==165 & sap$Time %in% c(12,12.1,12.2,12.3,12.4,12.5,13,13.1,13.2,13.3,13.4,13.5, 14), ],mean)

sapply(sap[sap$Day==166 & sap$Time %in% c(12,12.1,12.2,12.3,12.4,12.5,13,13.1,13.2,13.3,13.4,13.5, 14), ],mean)

以下是数据的样子：

Day Time    StomCond_Trunc
165 12      33.57189926
165 12.1    50.29437636
165 12.2    35.59876214
165 12.3    24.39879768

推荐答案

尝试：

aggregate(StomCond_Trunc~Day,data=subset(sap,Time>=12 & Time<=14),mean)

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