R: Function to perform t-test on all possible combinations of columns in a dataframe

Sometimes I need to perform a t-test on all possible combinations of the columns of a data-frame and rather than computing them all one by one, I wrote this small function:


ttest_all_possible  <- function(dataframe) {
    nr_columns = dim(dataframe)[2]
    results <- matrix(NA, nr_columns, nr_columns)
    for (i in seq(1, nr_columns)){
        for (j in seq(1, nr_columns)){
            results[i, j] <- t.test(dataframe[,i], dataframe[,j])$p.value
        }
    }
    return(results)
}

Works fine:
> test <- cbind(rnorm(10),rnorm(10), rnorm(10))
> test
             [,1]       [,2]       [,3]
 [1,]  0.64061950 -0.5643179  0.7450485
 [2,]  1.90703328 -0.8000197  0.2444611
 [3,]  0.96346636 -0.6278075  0.1283072
 [4,] -0.25758024 -0.9657888 -0.8832595
 [5,]  0.36934381  1.4149775  0.8837320
 [6,]  0.60584130  0.2556500 -0.2437533
 [7,] -0.24559562 -0.7774171  0.1279253
 [8,] -1.53276425  0.3557177  0.1611155
 [9,] -1.55474156  0.3488891  0.1025763
[10,] -0.08366046 -0.2823561  1.3618903
> ttest_all_possible(test)
          [,1]      [,2]      [,3]
[1,] 1.0000000 0.5603004 0.6495045
[2,] 0.5603004 1.0000000 0.1817692
[3,] 0.6495045 0.1817692 1.0000000

How to substutitute characters in all files of a directory using regex and perl

perl -i -pe 's/CharacterToSubstiture/SubstituteWithThis/g' myfilename

Example:
Imagine I have got these two files:

shopping_list_groceries.txt:
- 2 apples
- 3 red paprika

shopping_list_clothes.txt:

- 2 pairs of socks

- 1 red t-shirt

And now I decide to not like red any more, but to prefer green:

perl -i -pe 's/red/green/g' shopping_list*txt

The text files now look like this:
shopping_list_groceries.txt:
- 2 apples
- 3 green paprika

shopping_list_clothes.txt:

- 2 pairs of socks

- 1 green t-shirt

What does the one-liner do?

perl # use perl :)

-i # change in the file, if you skip this part, the changes will be printed to stdout

-pe # I don't know

's/red/green/g' # RegEx: 

                 's # Substitute...

                 /red # ...every occurence of the string "red"...

                 /green # ...with the string "green"...

                 /g' # ... everywhere ...

shopping_list*.txt # ...in all files starting with 'shopping_list' and ending with '.txt

How to print all the attributes of an object in python

from pprint import pprint
pprint (vars(my_object))     # e.g. class instance

This prints all the attributes/properties this object currently has in a neat way.