[R] Creating a simple function

[Jeff Newmiller]

The dplyr::select function returns a special variety of data.frame called a tibble. The tibble has certain features designed to make it behave consistently when indexing is used. Specifically, the `[` operator always returns a tibble regardless of how many columns are indicated by the column index. This is unlike the conventional data frame which returns a vector when exactly one column is indicated by the column index, or a data.frame if more than one is indicated.

A syntax that consistently yields a column vector with both tibbles and data.frames is

dta[[ 1 ]]

so

ctab <- function(data) {
   CrossTable(data[[1]], data[[2]], prop.chisq = FALSE, prop.c = FALSE,
prop.t = FALSE, format = "SPSS")
}

should work.

On September 20, 2019 10:59:46 AM PDT, Duncan Murdoch <murdoch.duncan using gmail.com> wrote:
>On 20/09/2019 11:30 a.m., Zachary Lim wrote:
>> Hi,
>> 
>> I'm trying to create a simple function that takes a dataframe as its
>only argument. I've been using gmodels::CrossTable, but it requires a
>lot of arguments, e.g.:
>> 
>> #this runs fine
>> CrossTable(data$col1, data$col2, prop.chisq = FALSE, prop.c = FALSE,
>prop.t = FALSE, format = "SPSS")
>> 
>> Moreover, I wanted to make it compatible with piping, so I decided to
>create the following function:
>> 
>> ctab <- function(data) {
>>    CrossTable(data[,1], data[,2], prop.chisq = FALSE, prop.c = FALSE,
>prop.t = FALSE, format = "SPSS")
>> }
>> 
>> When I try to use this function, however, I get the following error:
>> 
>> #this results in 'Error: Must use a vector in `[`, not an object of
>class matrix.'
>> data %>% select(col1, col2) %>% ctab()
>> 
>> I tried searching online but couldn't find much about that error
>(except for in specific and unrelated cases). Moreover, when I created
>a very simple dataset, it turns out there's no problem:
>> 
>> #this runs fine
>> data.frame(C1 = c('x','y','x','y'), C2 = c('a','a','b','b')) %>%
>ctab()
>> 
>> 
>> Is this a problem with my function or the data? If it's the data, why
>does directly calling CrossTable work?
>
>Presumably  data %>% select(col1, col2)  isn't giving you a dataframe. 
>However, you haven't given us a reproducible example, so I can't tell 
>you what it's doing.  But that's where you should look.
>
>Duncan Murdoch
>
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-- 
Sent from my phone. Please excuse my brevity.