Maciej B. - 3 years ago 192

R Question

I would like to use Chi-square for testing set of data. How to do it, using loop for or sapply.

This is a set of sample data:

`n<-40`

set.seed(1)

data <- data.frame(v1.1=sample(c('0','1'),n,replace=T),v1.2=sample(c('0','1'),n,replace=T),v1.3=sample(c('0','1'),n,replace=T),v1.4=sample(c('0','1'),n,replace=T),v1.5=sample(c('0','1'),n,replace=T),m1=sample(c('1','2'),n,replace=T))

I would like to test all variables named v1.x with variable m1. That's all.

I want

`chisq.test(table(data$v1.1,data$m1))`

chisq.test(table(data$v1.2,data$m1))

chisq.test(table(data$v1.3,data$m1))

chisq.test(table(data$v1.4,data$m1))

chisq.test(table(data$v1.5,data$m1))

I found this topic, but for me and for now it's too difficult.

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Answer Source

You can just use `lapply`

to loop through the variables.

```
myTests <- lapply(data[-length(data)], function(x) chisq.test(table(x, data$m1)))
```

This returns a named list, with the changin variable as the name of each list item.

```
names(myTests)
[1] "v1.1" "v1.2" "v1.3" "v1.4" "v1.5"
```

Then access each with `myTests[[1]]`

or `myTests[["v1.1"]]`

. These return

```
Pearson's Chi-squared test with Yates' continuity correction
data: table(x, data$m1)
X-squared = 0, df = 1, p-value = 1
```

Then, to pull out components from the individual tests, use `names(myTests[[1]]`

and `str(myTests[[1]])`

to inspect the contents. `myTests[[1]]$p.value`

, for example, will pull out the p.value from the first test and `unlist(sapply(myTests, "[", "p.value"))`

will return a named vector with p-values from all of the tests.

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