How I pass string inside R function - r

Question

I have a df and I would like to do a function with the names of header and return linear models.
I'm trying this:
a <- function(j,k){
reg1 <- lm(data$j ~ data$k)
summary(reg1)
}
a(j="hour",k="score")
It's NULL for 'data$j'

Answer 1

You cannot use $ when passing column name as variable. Here are couple of ways in which you can do this.
Use reformulate to create a formula object
a <- function(data, j,k){
reg1 <- lm(reformulate(k, j), data = data)
summary(reg1)
}
lm also accepts formula as string so you don't necessarily need to convert it into formula object.
a <- function(data, j,k){
reg1 <- lm(sprintf('%s~%s', j, k), data = data)
summary(reg1)
}
You can call this as :
a(mtcars, 'mpg', 'cyl')
#Call:
#lm(formula = sprintf("%s~%s", j, k), data = data)
#Residuals:
# Min 1Q Median 3Q Max
#-4.9814 -2.1185 0.2217 1.0717 7.5186
#Coefficients:
# Estimate Std. Error t value Pr(>|t|)
#(Intercept) 37.8846 2.0738 18.27 < 2e-16 ***
#cyl -2.8758 0.3224 -8.92 6.11e-10 ***
#---
#Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
#Residual standard error: 3.206 on 30 degrees of freedom
#Multiple R-squared: 0.7262, Adjusted R-squared: 0.7171
#F-statistic: 79.56 on 1 and 30 DF, p-value: 6.113e-10
Note that I added data as an additional argument in the function. It is generally a better practice to pass data object in the function rather than relying it to be evaluated in global environment.

Answer 2

Try this. If you are going tu use strings which are as variables in a dataframe, it is better to invoke them in a function using [[]]. Here the code of your function with slight changes:
a <- function(j,k){
reg1 <- lm(data[[j]] ~ data[[k]])
summary(reg1)
}
a(j="hour",k="score")
And a small example using iris dataset:
#Example
data=iris
#Code
a(j="Sepal.Length",k="Petal.Length")
You can further tune your function a if needed.