dplyr::manip: How to use string arguments (holding colnames) instead of column names

Question

The title describes pretty much what I want:

instead of:

filter(mtcars, cyl == 8)

I would like to use:

var <- "cyl"
filter(mtcars, var == 8)  # pseudocode

just like

mtcars[which(mtcars[,var]==8),]

I see that there are functions like starts_with() but IMHO none really suits for above rather simple application.

just saw that this is somewhat related to http://stackoverflow.com/questions/21208801/group-by-multiple-columns-in-dplyr-using-string-vector-input — Janhoo, Aug 01 '14 at 07:58
It's not currently supported, but I'm working on it: https://github.com/hadley/dplyr/issues/352 — hadley, Aug 01 '14 at 13:30
This feature is now implemented. No workaround neccessary. To get around non-standard evaluation, use the `manip_()` flavor, e.g. `filter_()`. `vignette("nse")` elaborates on that. Thanks @hadley — Janhoo, Oct 20 '15 at 12:34

score 3 · Accepted Answer · answered Aug 01 '14 at 11:15

3

Try this:

mtcars %>% do(filter(., .[[var]] == 8))

answered Aug 01 '14 at 11:15

G. Grothendieck

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akrun · Answer 2 · 2014-08-01T08:05:32.100

2

eval(substitute(filter(mtcars, var == 8),list(var=as.name(var))))%>%
head(2)
#    mpg cyl disp  hp drat   wt  qsec vs am gear carb
# 1 18.7   8  360 175 3.15 3.44 17.02  0  0    3    2
# 2 14.3   8  360 245 3.21 3.57 15.84  0  0    3    4

filter(mtcars, get(var, envir=as.environment(mtcars)) == 8) #should also work but not recommended

edited Aug 01 '14 at 08:05

answered Aug 01 '14 at 08:00

akrun

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From you answer I conclude that currently dplyr does not support string arguments. Right? – Janhoo Aug 01 '14 at 08:07
@Jan, Yes, if i am not mistaken. – akrun Aug 01 '14 at 08:07
Well, then this kind of answers my question. Although not in a very satisfactory manner. @akrun Not your fault, though. Thanks mate. – Janhoo Aug 01 '14 at 08:12

score 0 · Answer 3 · answered Aug 01 '14 at 15:43

0

Here's one more way with do.call:

do.call(filter, list(mtcars, bquote(.(as.name(var)) == 8)))

answered Aug 01 '14 at 15:43

Matthew Plourde

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dplyr::manip: How to use string arguments (holding colnames) instead of column names

3 Answers3