How to convert R formula to text?

r r-formula

I have trouble working with formula as with text. What I'm trying to do is to concatenate the formula to the title of the graph. However, when I try to work with the formula as with text, I fail:

model <- lm(celkem ~ rok + mesic)
formula(model)
# celkem ~ rok + mesic

This is fine. Now I want to build string like "my text celkem ~ rok + mesic" - this is where the problem comes:

paste("my text", formula(model))
# [1] "my text ~"           "my text celkem"      "my text rok + mesic"

paste("my text", as.character(formula(model)))
# [1] "my text ~"           "my text celkem"      "my text rok + mesic"

paste("my text", toString(formula(model)))
# [1] "my text ~, celkem, rok + mesic"

Now I see there is a sprint function in package gtools, but I think this is such a basic thing that it deserves a solution within the default environment!!

Solution 1:

A short solution from the package formula.tools, as a function as.character.formula:

frm <- celkem ~ rok + mesic
Reduce(paste, deparse(frm))
# [1] "celkem ~ rok + mesic"

library(formula.tools)
as.character(frm)
# [1] "celkem ~ rok + mesic"

Reduce might be useful in case of long formulas:

frm <- formula(paste("y ~ ", paste0("x", 1:12, collapse = " + ")))

deparse(frm)
# [1] "y ~ x1 + x2 + x3 + x4 + x5 + x6 + x7 + x8 + x9 + x10 + x11 + "
# [2] "    x12"                                                      
Reduce(paste, deparse(frm))
# [1] "y ~ x1 + x2 + x3 + x4 + x5 + x6 + x7 + x8 + x9 + x10 + x11 +      x12"

Which is because of width.cutoff = 60L in ?deparse.

Solution 2:

Try format :

paste("my text", format(frm))
## [1] "my text celkem ~ rok + mesic"

Solution 3:

Simplest solution covering everything:

f <- formula(model)
paste(deparse(f, width.cutoff = 500), collapse="")

Solution 4:

or as an alternative to Julius's version (note: your code was not self-contained)

celkem = 1
rok = 1
mesic = 1
model <- lm(celkem ~ rok + mesic)
paste("my model ", deparse(formula(model)))

Solution 5:

R 4.0.0 (released 2020-04-24) introduced deparse1 which never splits the result into multiple strings:

f <- y ~ a + b + c + d + e + f + g + h + i + j + k + l + m + n + o + 
     p + q + r + s + t + u + v + w + x + y + z
deparse(f)
# [1] "y ~ a + b + c + d + e + f + g + h + i + j + k + l + m + n + o + " "    p + q + r + s + t + u + v + w + x + y + z"                   
deparse1(f)
# [1] "y ~ a + b + c + d + e + f + g + h + i + j + k + l + m + n + o + p + q + r + s + t + u + v + w + x + y + z"

However, it still has a width.cutoff argument (default (an maximum): 500) after which linebreaks are introduced but with lines separated by collapse (default: " ") not \n, leaving extra white whitespace (even with collapse = "") (use gsub to remove them if needed, see Ross D's answer):

> f <- rlang::parse_expr( paste0("y~", paste0(rep(letters, 20), collapse="+")))
> deparse1(f, collapse = "")
[1] "y ~ a + b + c + d + e + f + g + h + i + j + k + l + m + n + o + p + q + r + s + t + u + v + w + x + y + z + a + b + c + d + e + f + g + h + i + j + k + l + m + n + o + p + q + r + s + t + u + v + w + x + y + z + a + b + c + d + e + f + g + h + i + j + k + l + m + n + o + p + q + r + s + t + u + v + w + x + y + z + a + b + c + d + e + f + g + h + i + j + k + l + m + n + o + p + q + r + s + t + u + v + w + x + y + z + a + b + c + d + e + f + g + h + i + j + k + l + m + n + o + p + q + r + s + t + u +     v + w + x + y + z + a + b + c + d + e + f + g + h + i + j + k + l + m + n + o + p + q + r + s + t + u + v + w + x + y + z + a + b + c + d + e + f + g + h + i + j + k + l + m + n + o + p + q + r + s + t + u + v + w + x + y + z + a + b + c + d + e + f + g + h + i + j + k + l + m + n + o + p + q + r + s + t + u + v + w + x + y + z + a + b + c + d + e + f + g + h + i + j + k + l + m + n + o + p + q + r + s + t + u + v + w + x + y + z + a + b + c + d + e + f + g + h + i + j + k + l + m + n + o + p +     q + r + s + t + u + v + w + x + y + z + a + b + c + d + e + f + g + h + i + j + k + l + m + n + o + p + q + r + s + t + u + v + w + x + y + z + a + b + c + d + e + f + g + h + i + j + k + l + m + n + o + p + q + r + s + t + u + v + w + x + y + z + a + b + c + d + e + f + g + h + i + j + k + l + m + n + o + p + q + r + s + t + u + v + w + x + y + z + a + b + c + d + e + f + g + h + i + j + k + l + m + n + o + p + q + r + s + t + u + v + w + x + y + z + a + b + c + d + e + f + g + h + i + j + k +     l + m + n + o + p + q + r + s + t + u + v + w + x + y + z + a + b + c + d + e + f + g + h + i + j + k + l + m + n + o + p + q + r + s + t + u + v + w + x + y + z + a + b + c + d + e + f + g + h + i + j + k + l + m + n + o + p + q + r + s + t + u + v + w + x + y + z + a + b + c + d + e + f + g + h + i + j + k + l + m + n + o + p + q + r + s + t + u + v + w + x + y + z + a + b + c + d + e + f + g + h + i + j + k + l + m + n + o + p + q + r + s + t + u + v + w + x + y + z + a + b + c + d + e + f +     g + h + i + j + k + l + m + n + o + p + q + r + s + t + u + v + w + x + y + z"

To use it in R < 4.0.0 use backports (recommended) or copy it's implementation:

#  Part of the R package, https://www.R-project.org
#
#  Copyright (C) 1995-2019 The R Core Team
#
#  This program is free software; you can redistribute it and/or modify
#  it under the terms of the GNU General Public License as published by
#  the Free Software Foundation; either version 2 of the License, or
#  (at your option) any later version.
#
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#
#  A copy of the GNU General Public License is available at
#  https://www.R-project.org/Licenses/

deparse1 <- function (expr, collapse = " ", width.cutoff = 500L, ...) 
    paste(deparse(expr, width.cutoff, ...), collapse = collapse)