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Questions
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516,172 questions
2463
votes
23
answers
488k
views
How to make a great R reproducible example
When discussing performance with colleagues, teaching, sending a bug report or searching for guidance on mailing lists and here on Stack Overflow, a reproducible example is often asked and always ...
1512
votes
21
answers
1.4m
views
Sort (order) data frame rows by multiple columns
I want to sort a data frame by multiple columns. For example, with the data frame below I would like to sort by column 'z' (descending) then by column 'b' (ascending):
dd <- data.frame(b = factor(c(...
- 43.6k
993
votes
30
answers
2.2m
views
How do I replace NA values with zeros in an R dataframe?
I have a data frame and some columns have NA values.
How do I replace these NA values with zeroes?
- 37k
1052
votes
25
answers
2.0m
views
Drop data frame columns by name
I have a number of columns that I would like to remove from a data frame. I know that we can delete them individually using something like:
df$x <- NULL
But I was hoping to do this with fewer ...
- 40.4k
1570
votes
14
answers
1.9m
views
How to join (merge) data frames (inner, outer, left, right)
Given two data frames:
df1 = data.frame(CustomerId = c(1:6), Product = c(rep("Toaster", 3), rep("Radio", 3)))
df2 = data.frame(CustomerId = c(2, 4, 6), State = c(rep("Alabama&...
- 25k
1094
votes
20
answers
2.4m
views
Remove rows with all or some NAs (missing values) in data.frame
I'd like to remove the lines in this data frame that:
a) contain NAs across all columns. Below is my example data frame.
gene hsap mmul mmus rnor cfam
1 ENSG00000208234 0 NA NA ...
- 12.1k
650
votes
27
answers
1.3m
views
Convert a list to a data frame
I have a nested list of data. Its length is 132 and each item is a list of length 20. Is there a quick way to convert this structure into a data frame that has 132 rows and 20 columns of data?
Here is ...
- 40.4k
1157
votes
12
answers
444k
views
Grouping functions (tapply, by, aggregate) and the *apply family
Whenever I want to do something "map"py in R, I usually try to use a function in the apply family.
However, I've never quite understood the differences between them -- how {sapply, lapply, etc.} ...
- 30.6k
519
votes
38
answers
437k
views
How to find the statistical mode?
In R, mean() and median() are standard functions which do what you'd expect. mode() tells you the internal storage mode of the object, not the value that occurs the most in its argument. But is there ...
- 22.3k
457
votes
35
answers
276k
views
Elegant way to check for missing packages and install them?
I seem to be sharing a lot of code with coauthors these days. Many of them are novice/intermediate R users and don't realize that they have to install packages they don't already have.
Is there an ...
- 33.1k
550
votes
28
answers
144k
views
Tricks to manage the available memory in an R session
What tricks do people use to manage the available memory of an interactive R session? I use the functions below [based on postings by Petr Pikal and David Hinds to the r-help list in 2004] to list (...
694
votes
17
answers
1.9m
views
Plot two graphs in a same plot
I would like to plot y1 and y2 in the same plot.
x <- seq(-2, 2, 0.05)
y1 <- pnorm(x)
y2 <- pnorm(x, 1, 1)
plot(x, y1, type = "l", col = "red")
plot(x, y2, type = "l", col = "green")
But ...
- 26.3k
723
votes
19
answers
1.1m
views
How should I deal with "package 'xxx' is not available (for R version x.y.z)" warning?
I tried to install a package, using
install.packages("foobarbaz")
but received the warning
Warning message:
package 'foobarbaz' is not available (for R version x.y.z)
Why doesn't R think that the ...
- 122k
480
votes
21
answers
1.5m
views
How to rename a single column in a data.frame?
I know if I have a data frame with more than 1 column, then I can use
colnames(x) <- c("col1","col2")
to rename the columns. How to do this if it's just one column?
Meaning a ...
- 28.3k
926
votes
8
answers
1.7m
views
Rotating and spacing axis labels in ggplot2
I have a plot where the x-axis is a factor whose labels are long. While probably not an ideal visualization, for now I'd like to simply rotate these labels to be vertical. I've figured this part out ...
- 43.6k
609
votes
17
answers
1.2m
views
Create an empty data.frame
I'm trying to initialize a data.frame without any rows. Basically, I want to specify the data types for each column and name them, but not have any rows created as a result.
The best I've been able ...
- 17.6k
521
votes
19
answers
1.0m
views
How to sum a variable by group
I have a data frame with two columns. First column contains categories such as "First", "Second", "Third", and the second column has numbers that represent the number of times I saw the specific ...
- 10.4k
493
votes
21
answers
1.7m
views
Counting the number of elements with the values of x in a vector
I have a vector of numbers:
numbers <- c(4,23,4,23,5,43,54,56,657,67,67,435,
453,435,324,34,456,56,567,65,34,435)
How can I have R count the number of times a value x appears in the ...
- 4,933
494
votes
19
answers
2.0m
views
Changing column names of a data frame
I have a data frame called "newprice" (see below) and I want to change the column names in my program in R.
> newprice
Chang. Chang. Chang.
1 100 36 136
2 120 -33 ...
- 5,465
610
votes
16
answers
458k
views
Drop unused factor levels in a subsetted data frame
I have a data frame containing a factor. When I create a subset of this dataframe using subset or another indexing function, a new data frame is created. However, the factor variable retains all of ...
- 27.6k
975
votes
9
answers
396k
views
What are the differences between "=" and "<-" assignment operators?
What are the differences between the assignment operators = and <- in R?
I know that operators are slightly different, as this example shows
x <- y <- 5
x = y = 5
x = y <- 5
x <- y = ...
- 60.8k
716
votes
14
answers
1.2m
views
How to convert a factor to integer\numeric without loss of information?
When I convert a factor to a numeric or integer, I get the underlying level codes, not the values as numbers.
f <- factor(sample(runif(5), 20, replace = TRUE))
## [1] 0.0248644019011408 0....
- 10k
702
votes
14
answers
461k
views
How can I view the source code for a function?
I want to look at the source code for a function to see how it works. I know I can print a function by typing its name at the prompt:
> t
function (x)
UseMethod("t")
<bytecode: 0x2332948>
&...
- 177k
547
votes
14
answers
1.5m
views
How to change legend title in ggplot
I have the following plot like below. It was created with this command:
library(ggplot2)
df <- data.frame(cond = factor(rep(c("A", "B"), each = 200)),
rating =...
- 64.5k
580
votes
13
answers
743k
views
How to find out which package version is loaded in R?
I am in a process of figuring out how to use my university cluster. It has 2 versions of R installed. System wide R 2.11 (Debian 6.0) and R 2.14.2 in non-standard location.
I am trying to use MPI ...
- 11.5k
687
votes
12
answers
608k
views
How to unload a package without restarting R
I'd like to unload a package without having to restart R (mostly because restarting R as I try out different, conflicting packages is getting frustrating, but conceivably this could be used in a ...
- 73.1k
575
votes
12
answers
287k
views
Quickly reading very large tables as dataframes
I have very large tables (30 million rows) that I would like to load as a dataframes in R. read.table() has a lot of convenient features, but it seems like there is a lot of logic in the ...
- 6,075
689
votes
11
answers
348k
views
The difference between bracket [ ] and double bracket [[ ]] for accessing the elements of a list or dataframe
R provides two different methods for accessing the elements of a list or data.frame: [] and [[]].
What is the difference between the two, and when should I use one over the other?
- 17.7k
426
votes
15
answers
411k
views
How can I trim leading and trailing white space?
I am having some trouble with leading and trailing white space in a data.frame.
For example, I look at a specific row in a data.frame based on a certain condition:
> myDummy[myDummy$country == c(&...
- 11.9k
318
votes
24
answers
466k
views
How to change facet labels?
I have used the following ggplot command:
ggplot(survey, aes(x = age)) + stat_bin(aes(n = nrow(h3), y = ..count.. / n), binwidth = 10)
+ scale_y_continuous(formatter = "percent", breaks = c(0, 0.1, ...
- 14.9k
458
votes
14
answers
728k
views
Side-by-side plots with ggplot2
I would like to place two plots side by side using the ggplot2 package, i.e. do the equivalent of par(mfrow=c(1,2)).
For example, I would like to have the following two plots show side-by-side with ...
- 43.6k
307
votes
31
answers
160k
views
Determine path of the executing script
I have a script called foo.R that includes another script other.R, which is in the same directory:
#!/usr/bin/env Rscript
message("Hello")
source("other.R")
But I want R to find that other.R no ...
- 66.6k
405
votes
18
answers
774k
views
Convert data.frame columns from factors to characters
I have a data frame. Let's call him bob:
> head(bob)
phenotype exclusion
GSM399350 3- 4- 8- 25- 44+ 11b- 11c- 19- NK1.1- Gr1- TER119-
GSM399351 3- 4- 8- 25-...
- 11.1k
375
votes
21
answers
729k
views
How can I remove an element from a list?
I have a list and I want to remove a single element from it. How can I do this?
I've tried looking up what I think the obvious names for this function would be in the reference manual and I haven't ...
- 18.1k
403
votes
16
answers
606k
views
Order Bars in ggplot2 bar graph
I am trying to make a bar graph where the largest bar would be nearest to the y axis and the shortest bar would be furthest. So this is kind of like the Table I have
Name Position
1 James ...
- 9,487
456
votes
14
answers
720k
views
Sample random rows in dataframe
I am struggling to find the appropriate function that would return a specified number of rows picked up randomly without replacement from a data frame in R language? Can anyone help me out?
- 9,423
351
votes
18
answers
632k
views
Split data frame string column into multiple columns
I'd like to take data of the form
before = data.frame(attr = c(1,30,4,6), type=c('foo_and_bar','foo_and_bar_2'))
attr type
1 1 foo_and_bar
2 30 foo_and_bar_2
3 4 foo_and_bar
4 ...
- 4,164
462
votes
13
answers
490k
views
Write lines of text to a file in R
In the R scripting language, how do I write lines of text, e.g., the following two lines
Hello
World
to a file named "output.txt"?
- 25k
362
votes
19
answers
604k
views
ggplot with 2 y axes on each side and different scales
I need to plot a bar chart showing counts and a line chart showing rate all in one chart, I can do both of them separately, but when I put them together, I scale of the first layer (i.e. the geom_bar) ...
- 24.9k
463
votes
12
answers
1.8m
views
Extracting specific columns from a data frame
I have an R data frame with 6 columns, and I want to create a new data frame that only has three of the columns.
Assuming my data frame is df, and I want to extract columns A, B, and E, this is the ...
- 6,740
771
votes
7
answers
95k
views
How can we make xkcd style graphs?
Apparently, folk have figured out how to make xkcd style graphs in Mathematica and in LaTeX. Can we do it in R? Ggplot2-ers? A geom_xkcd and/or theme_xkcd?
I guess in base graphics, par(xkcd=TRUE)? ...
- 9,386
308
votes
23
answers
246k
views
Split a vector into chunks
I have to split a vector into n chunks of equal size in R. I couldn't find any base function to do that. Also Google didn't get me anywhere. Here is what I came up with so far;
x <- 1:10
n <- 3
...
- 3,867
488
votes
12
answers
996k
views
How can two strings be concatenated?
How can I concatenate (merge, combine) two values?
For example I have:
tmp = cbind("GAD", "AB")
tmp
# [,1] [,2]
# [1,] "GAD" "AB"
My goal is to concatenate the two values in "tmp" to one string:...
- 5,585
678
votes
7
answers
1.2m
views
Run R script from command line
I have a file, called a.r, it has a chmod of 755,
sayHello <- function(){
print('hello')
}
sayHello()
How can I run this via command-line?
- 19.9k
918
votes
5
answers
172k
views
data.table vs dplyr: can one do something well the other can't or does poorly?
Overview
I'm relatively familiar with data.table, not so much with dplyr. I've read through some dplyr vignettes and examples that have popped up on SO, and so far my conclusions are that:
data....
- 52.8k
642
votes
8
answers
977k
views
676
votes
8
answers
185k
views
What is the difference between require() and library()?
What is the difference between require() and library()?
- 9,654
385
votes
16
answers
574k
views
Extracting the last n characters from a string in R
How can I get the last n characters from a string in R?
Is there a function like SQL's RIGHT?
- 6,824
537
votes
11
answers
450k
views
Folder management with r : Check existence of directory and create it if it doesn't exist
I often find myself writing R scripts that generate a lot of output. I find it cleaner to put this output into its own directory(s). What I've written below will check for the existence of a directory ...
- 69.4k
371
votes
16
answers
326k
views
Measuring function execution time in R
Is there a standardized way in R of measuring execution time of function?
Obviously I can take system.time before and after execution and then take the difference of those, but I would like to know ...
- 3,711
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