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Collection

R Language Frequently Asked Questions

The questions that get asked repeatedly, gathered together in one place. What’s a question every R programmer asks at some point? Add it here! Grab questions from the tag to get them added visibility. This collection also serves as a repository for excellent Q&As for curators to propose as duplicate targets for commonly asked questions.

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19 posts in this collection
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2464 votes
23 answers
469k views

How to make a great R reproducible example

Andrie's user avatar
Andrie
This question helps with creating a minimal, but complete and verifiable example that can be reproduced by others in order to answer your question.
M--'s user avatar
M--
251 votes
9 answers
335k views

Reshaping data.frame from wide to long format

mropa's user avatar
mropa
Common data wrangling task
M--'s user avatar
M--
383 votes
15 answers
494k views

How to reshape data from long to wide format

Steve's user avatar
Steve
Common data wrangling task
M--'s user avatar
M--
50 votes
6 answers
58k views

Convert data from long format to wide format with multiple measure columns

colonel.triq's user avatar
colonel.triq
Common question
M--'s user avatar
M--
1547 votes
14 answers
1.8m views

How to join (merge) data frames (inner, outer, left, right)

Dan Goldstein's user avatar
Dan Goldstein
Common data wrangling task -- high-level post.
Maël's user avatar
Maël
977 votes
30 answers
2.1m views

How do I replace NA values with zeros in an R dataframe?

Renato Dinhani's user avatar
Renato Dinhani
High view count
Berthold's user avatar
Berthold
1500 votes
22 answers
1.4m views

Sort (order) data frame rows by multiple columns

Christopher DuBois's user avatar
Christopher DuBois
High view count
M--'s user avatar
M--
393 votes
16 answers
584k views

Order Bars in ggplot2 bar graph

Julio Diaz's user avatar
Julio Diaz
Users often struggle to affect the order in which ggplot plots data. This question contains several good ways to do that.
jdobres's user avatar
jdobres
708 votes
14 answers
1.1m views

How to convert a factor to integer\numeric without loss of information?

Adam SO's user avatar
Adam SO
High view count
Berthold's user avatar
Berthold
957 votes
9 answers
378k views

What are the differences between "=" and "<-" assignment operators?

csgillespie's user avatar
csgillespie
High view count
Berthold's user avatar
Berthold
371 votes
5 answers
642k views

Plotting two variables as lines using ggplot2 on the same graph

fmark's user avatar
fmark
Common misconception about ggplot and base R
Ian Campbell's user avatar
Ian Campbell
121 votes
5 answers
18k views

What are the differences between R's native pipe `|>` and the magrittr pipe `%>%`?

sieste's user avatar
sieste
It is important to be aware of the differences in the native pipe and that by magrittr
mhovd's user avatar
mhovd
371 votes
5 answers
642k views

Plotting two variables as lines using ggplot2 on the same graph

fmark's user avatar
fmark
Answer

The general approach is to convert the data to long format (using melt() from package reshape or reshape2) or gather()/pivot_longer() from the tidyr package: library("ggplot2") library("...

View answer
rcs's user avatar
rcs
Users accustomed to other plotting libraries often miss that ggplot is meant to work with "long" data, and this answer explains a simple example nicely.
jdobres's user avatar
jdobres
716 votes
19 answers
1.0m views

How should I deal with "package 'xxx' is not available (for R version x.y.z)" warning?

Richie Cotton's user avatar
Richie Cotton
Great canonical duplicate target for a common error
Ian Campbell's user avatar
Ian Campbell
311 votes
7 answers
69k views

Why are these numbers not equal?

dplanet's user avatar
dplanet
The question is asked repeatedly. Beginners often don't understand flaoting point arithmetic.
G5W's user avatar
G5W
158 votes
6 answers
54k views

Split comma-separated strings in a column into separate rows

RoyalTS's user avatar
RoyalTS
Very frequent question where users wish to separate comma separated string/column `c("a, b")` into separate rows `c("a", "b")`. This dup target mostly focuses on doing this within a `data.frame`.
Maël's user avatar
Maël
28 votes
11 answers
10k views

Expand ranges defined by "from" and "to" columns

edgester's user avatar
edgester
Common question about how to expand data where every row has a start and end date into repeated observations
SamR's user avatar
SamR
110 votes
10 answers
233k views

Problems when trying to load a package in R due to rJava

Pritam Kar's user avatar
Pritam Kar
Commonly encountered error
M--'s user avatar
M--
30 votes
2 answers
21k views

Understanding color scales in ggplot2

LulY's user avatar
LulY
Commonly used functions with ggplot2
M--'s user avatar
M--
2
  • Is it possible to change the order of the questions? "Reshaping data.frame from wide to long format", "How to reshape data from long to wide format", and "Convert data from long format to wide format with multiple measure columns" should be all next to each other.
    – Brian Diggs
    Commented Oct 25, 2023 at 22:42
  • 4
    @BrianDiggs thank you for this suggestion! I just made that change. Collective admins and Recognized Members can change the order of items in collections.
    – Sasha ♦
    Commented Oct 26, 2023 at 14:28