Create line graph comparing pre and post median values of two groups

Question

I have a dataframe with 2 cond, and 2 time points within each cond (pre and post). I am looking to create a line graph showing the pre and post MEDIAN values from the sc column from a group of subjects on both conds. I would also like there to be a line connecting the pre and post values on each cond. ie. Pre ------ Post for cond #1, and Pre ----- Post for cond #2.

Data:

convert

This is just a sample of the data. There are 11 subjects (id 1:11) in my data set for each condition at each time point. This is the best code I have so far:

id    cond    time    sc
1      1       0      400
2      1       0      370
1      1       1      300
2      1       1      302
1      2       0      402
2      2       0      380
1      2       1      220
2      2       1      203

Right now this code gives me all the points from each condition (cond) and not just one point showing the median values. Been searching online for quite a few hours today but can't find an example similar to what I'm trying to create.

Answer 1

喜欢这个？

d1 <- "id    cond    time    sc
1      1       0      400
2      1       0      370
1      1       1      300
2      1       1      302
1      2       0      402
2      2       0      380
1      2       1      220
2      2       1      203"
library("data.table")
d1 <- data.table(read.table(text=d1, header = TRUE))
d1[, "median" := median(sc), by=list(cond, time)]
library("ggplot2")
ggplot(d1, aes(x=time, y=median, color=factor(cond))) +
    geom_line() +
    geom_point()

，并提供：

我发现data.table是这类“分组”/“汇总”问题的最简单方法，但还有很多其他问题。

另外，请注意调用df，因为这会覆盖stats::df()。

Answer 2

在vanilla R中，您可以使用aggregate获得与@dardisco的data.tables解决方案相同的功能。

d1 <- ... as above ...
d2 <- read.table(text=d1, header=T)
d3 <- aggregate(sc ~ time + cond, d2, median)
require(ggplot2)
ggplot(d3) + geom_line(aes(x=time, y=sc, color=factor(cond))