for loop, error in model frame.default ... variable lengths differ

[snip]

What the poster probably wanted was something in the vein of

nm <- colnames(airquality)[1]
ff <- formula(bquote(.(as.name(nm))~Month))
aggregate(ff, airquality, mean, na.rm=T)

?Month ? ?Ozone
1 ? ? 5 23.61538
2 ? ? 6 29.44444
3 ? ? 7 59.11538
4 ? ? 8 59.96154
5 ? ? 9 31.44828

or perhaps to use an implicit loop (since looping seemed to be part of it all):

results <- lapply(c("Ozone", "Solar.R"), function(n) {
  aggregate(. ~ Month, airquality[, c(n, "Month")], mean, na.rm = TRUE)
  })

## print results
results


## untested code based on OPs original example
vars <- colnames(df)[c(10,12,16,18,20,21,24:29,45)]
results <- lapply(vars, function(n) {
  aggregate(. ~ x1 + x2 + x3, df[, c(n, "x1", "x2", "x3")], mean, na.rm = TRUE)
  })

## print results
results

Cheers,

Josh

--
Peter Dalgaard, Professor
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk ?Priv: PDalgd at gmail.com

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and provide commented, minimal, self-contained, reproducible code.

Joshua Wiley
Ph.D. Student, Health Psychology
Programmer Analyst II, Statistical Consulting Group
University of California, Los Angeles
https://joshuawiley.com/