One sample T-TEST IN R within groups [duplicate]

问题

I have been doing one sample t-tests in R but today I have got one big challenge. I have data grouped in by one variable and I want to perform a one sample t-test per group. I can do this perfectly well in SPSS but it's now a headache in R, whoever knows how to do this to assist.Sample scenario

Location=rep(c("Area_A","Area_B"),4) 
temp=rnorm(length(Location),34,5) 
sample_data=data.frame(Location,ph)
sample_data
Location       temp
1   Area_A 32.73782
2   Area_B 26.29996
3   Area_A 40.75101
4   Area_B 26.68309
5   Area_A 33.94259
6   Area_B 26.48326
7   Area_A 37.92506
8   Area_B 29.22532

Say the hypothesised mean in the above example is 35 ,the one sample t test would be,

t.test(sample_data$temp,mu=35)

which gives me

 One Sample t-test

data:  sample_data$ph
t = -1.6578, df = 7, p-value = 0.1413
alternative hypothesis: true mean is not equal to 35
95 percent confidence interval:
 27.12898 36.38304
sample estimates:
mean of x 
 31.75601

But this is for all the groups combined. I can do it in SPSS. Is there any way to do this in R with a line of code or if not possible with a single line of code, who can do this for me. Thanks in advance.

回答1:

One solution is to save t.test results per group as a list:

# reproducible results
set.seed(8)

# example data
Location=rep(c("Area_A","Area_B"),4) 
temp=rnorm(length(Location),34,5) 
sample_data=data.frame(Location,temp)

library(dplyr)

dt_res = sample_data %>%
  group_by(Location) %>%                       # for each group
  summarise(res = list(t.test(temp, mu=35)))   # run t.test and save results as a list

# see the list of results
dt_res$res  

# [[1]]
# 
# One Sample t-test
# 
# data:  temp
# t = -0.76098, df = 3, p-value = 0.502
# alternative hypothesis: true mean is not equal to 35
# 95 percent confidence interval:
#   29.93251 38.11170
# sample estimates:
#   mean of x 
# 34.0221 
# 
# 
# [[2]]
# 
# One Sample t-test
# 
# data:  temp
# t = -1.045, df = 3, p-value = 0.3728
# alternative hypothesis: true mean is not equal to 35
# 95 percent confidence interval:
#   26.37007 39.36331
# sample estimates:
#   mean of x 
# 32.86669

Another solution is to save t.test results per group as a dataframe:

library(dplyr)
library(tidyr)
library(broom)

sample_data %>%
  group_by(Location) %>%                       
  summarise(res = list(tidy(t.test(temp, mu=35)))) %>%
  unnest()

# # A tibble: 2 x 9
#   Location estimate statistic p.value parameter conf.low conf.high method            alternative
#    <fct>       <dbl>     <dbl>   <dbl>     <dbl>    <dbl>     <dbl> <chr>             <chr>      
# 1 Area_A       34.0    -0.761   0.502         3     29.9      38.1 One Sample t-test two.sided  
# 2 Area_B       32.9    -1.05    0.373         3     26.4      39.4 One Sample t-test two.sided

The philosophy in both approaches is the same. You group by Location and you perform a t.test for each group. It's all about what kind of output you prefer to have.

来源：https://stackoverflow.com/questions/51723869/one-sample-t-test-in-r-within-groups

标签

t-test