在数据帧中由几个组计算平均值和SD

时间：2014-12-21 09:16:07

标签： r mean standard-deviation

我有一组数据需要我计算描述性统计数据，例如Mean和SD。诀窍是我尝试使用两个分组变量来计算这些统计信息。最终的目标是显然用SD作为误差条绘制平均值，但我还是留下了最后的结果。我只能计算由1个变量分组的均值和SD。

我已经从我的数据集中添加了一些数据供大家了解我想要实现的目标。我希望为特定治疗的每个变量计算平均值和SD。例如，NBR的平均值和SD分别用于控制，低，中和高，而不是NBR中所有值的均值。

非常感谢任何帮助！

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"Epoch", "Index_Name", "value"), row.names = c(NA, -352L), class = "data.frame")

1 个答案:

答案 0 :(得分：0)

mean(df$value[df$Plot == 'control' & df$Index_Name == 'NBR'])
summary(df$value[df$Plot == 'control' & df$Index_Name == 'NBR'])

是你想要的吗？

df$Plot == 'control' & df$Index_Name == 'NBR'  可以选择控制＆＃39;和＆＃39; NBR＆＃39;

它返回逻辑变量，因此df$value[df$Plot =='control' & df$Index_Name == 'NBR']可以选择NBR和控制的值。

类似地，

mean(df$value[df$Plot == 'low' & df$Index_Name == 'NBR'])
mean(df$value[df$Plot == 'medium ' & df$Index_Name == 'NBR'])
mean(df$value[df$Plot == 'high' & df$Index_Name == 'NBR'])
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