R: Filter a Data Frame Based on Values in Two Columns
R: Filter a Data Frame Based on Values in Two Columns
Join the DZone community and get the full member experience.
Join For FreeI started with a data frame that looked like this:
> data <- read.csv("specdata/002.csv")
> # we'll just use a few rows to make it easier to see what's going on
> data[2494:2500,]
Date sulfate nitrate ID
2494 2007-10-30 3.25 0.902 2
2495 2007-10-31 NA NA 2
2496 2007-11-01 NA NA 2
2497 2007-11-02 6.56 1.270 2
2498 2007-11-03 NA NA 2
2499 2007-11-04 NA NA 2
2500 2007-11-05 6.10 0.772 2
We want to only return the rows which have a value in both the ‘sulfate’ and the ‘nitrate’ columns.
I initially tried to use the Filter function but wasn’t very successful:
> smallData <- data[2494:2500,] > Filter(function(x) !is.na(x$sulfate), smallData) Error in x$sulfate : $ operator is invalid for atomic vectors
I’m not sure that Filter is designed to filter data frames – it seems more appropriate for lists or vectors – so I ended up filtering the data frame using what I think is called an extract operation:
> smallData[!is.na(smallData$sulfate) & !is.na(smallData$nitrate),] Date sulfate nitrate ID 2494 2007-10-30 3.25 0.902 2 2497 2007-11-02 6.56 1.270 2 2500 2007-11-05 6.10 0.772 2
The code inside the square brackets returns a collection indicating whether or not we should return each row:
> !is.na(smallData$sulfate) & !is.na(smallData$nitrate) [1] TRUE FALSE FALSE TRUE FALSE FALSE TRUE
which is equivalent to doing this:
> smallData[c(TRUE, FALSE, FALSE, TRUE, FALSE, FALSE, TRUE),] Date sulfate nitrate ID 2494 2007-10-30 3.25 0.902 2 2497 2007-11-02 6.56 1.270 2 2500 2007-11-05 6.10 0.772 2
We put a comma after the list of true/false values to indicate that we want to return all the columns otherwise we’d get this error:
> smallData[c(TRUE, FALSE, FALSE, TRUE, FALSE, FALSE, TRUE)] Error in `[.data.frame`(smallData, c(TRUE, FALSE, FALSE, TRUE, FALSE, : undefined columns selected
We could filter the columns as well if we wanted to:
> smallData[c(TRUE, FALSE, FALSE, TRUE, FALSE, FALSE, TRUE), c(1,2)] Date sulfate 2494 2007-10-30 3.25 2497 2007-11-02 6.56 2500 2007-11-05 6.10
As is no doubt obvious, I don’t know much R so if there’s a better way to do anything please let me know.
The full code is on github if you’re interested in seeing it in context.
Like This Article? Read More From DZone
Published at DZone with permission of Mark Needham , DZone MVB. See the original article here.
Opinions expressed by DZone contributors are their own.
{{ parent.title || parent.header.title}}
{{ parent.tldr }}
{{ parent.linkDescription }}
{{ parent.urlSource.name }}