wowdavers wowdavers - 2 months ago 9
R Question

Conducting a t-test with a grouping variable

Getting started on an assignment with R, and I haven't really worked with it before, so apologies if this is basic.

brain
is an excel dataframe. Its format is as follows (for an odd 40-some rows):

para1 para2 para3 para4 para5 para6 para7
FF 133 132 124 118 64.5 816932

highVAL = ifelse(brain$para2>=130,1, 0)


highVAL gives me a vector of 1's and 0's, categorized by para2.

I'm looking to perform a t-test on the mean para7 between two sets: rows that have para2 > 130 and those that have para2 < 130.

In Python, I would construct two new arrays and append values in, and perform a t-test there. Not sure how I would go about it in R.

Answer

You're closer than you think! Your highVAL variable should be added as a new column to the brain data frame:

brain$highVAL <- brain$FSIQ >= 130

This adds a true/false column to the dataset. Then you can run the test using t-test's formula interface:

result <- t.test(MRIcount ~ highVAL, data = brain)