Error assigning a value to a constructed variable in R

Question

I'm fairly new to R programming. Can someone say why this code keeps giving an error : paste0("emissions_for_",yr) <- sum(nei_tst[,var][select_obs], na.rm=TRUE)

(nei_tst is a dataframe)
(var is a variable that was assigned the name of one column in that dataframe)
select_obs is a variable with logical elements (result of test : yr == "1999")

I get the foll. error : Error in paste0("emissions_for_", yr) <- sum(nei_tst[, var][select_obs], : target of assignment expands to non-language object

Without a reproducible example, it's not easy to provide you with specifics. I think you want something like tapply(nei_tst[,var], nei_tst$yr, sum, na.rm=TRUE) will give you the result you want. Building variable names like they are strings is just not a good idea in R and often makes things much more difficult to work with. I strongly suggest you avoid this strategy. — MrFlick
– MrFlick, Commented Jan 21, 2015 at 20:05

Sven Hohenstein · Accepted Answer · 2016-10-15 05:26:27Z

1

You have to use assign if the name of the object is stored as a character string:

assign(paste0("emissions_for_",yr), sum(nei_tst[,var][select_obs], na.rm=TRUE))

However, creating multiple variables dynamically to store multiple values in not good R style. You should store all related values in a single object, e.g., a list or a data frame.

edited Oct 15, 2016 at 5:26

answered Jan 21, 2015 at 20:05

Sven Hohenstein

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2 Comments

Sven Hohenstein Over a year ago

@MrFlick Agreed. I added a comment.

Robert Over a year ago

Thanks guys...as simple as that ?!! (Mr. Flick, I think you actually helped me answer another question as well).

Scott C Wilson · Accepted Answer · 2015-01-21 20:09:08Z

0

Might you not be better off to create a dataframe, and index by year?

emissions <- data.frame(yr, sum(nei_tst[,var][select_obs], na.rm=TRUE))

answered Jan 21, 2015 at 20:09

Scott C Wilson

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