Selecting Multiple Columns by Name without having to Type each name

Question

How do I select multiple columns by name without having to type out each name.

For example I have the following code:

CTDB[, c(
"ENJOY_TV_RADIO_CHILD", 
"ENJOY_FMLY_CLOSE_FRND_CHILD", 
"ENJOY_HOBBIES_CHILD", 
"ENJOY_FAV_MEAL_CHILD",
"ENJOY_SHOWER_CHILD", 
"ENJOY_SCENT_CHILD", 
"ENJOY_PPL_SMILE_CHILD", 
"ENJOY_LOOK_SMART_CHILD", 
"ENJOY_READ_CHILD", 
"ENJOY_FAV_DRINK_CHILD", 
"ENJOY_SMALL_THINGS_CHILD", 
"ENJOY_LANDSCAPE_CHILD", 
"ENJOY_HELP_OTHR_CHILD", 
"ENJOY_PRAISE_CHILD")] <-revalue(as.matrix(CTDB[, c(
"ENJOY_TV_RADIO_CHILD", 
"ENJOY_FMLY_CLOSE_FRND_CHILD",
"ENJOY_HOBBIES_CHILD", 
"ENJOY_FAV_MEAL_CHILD", 
"ENJOY_SHOWER_CHILD", 
"ENJOY_SCENT_CHILD", 
"ENJOY_PPL_SMILE_CHILD", 
"ENJOY_LOOK_SMART_CHILD", 
"ENJOY_READ_CHILD", '
"ENJOY_FAV_DRINK_CHILD", 
"ENJOY_SMALL_THINGS_CHILD", 
"ENJOY_LANDSCAPE_CHILD", 
"ENJOY_HELP_OTHR_CHILD", 
"ENJOY_PRAISE_CHILD")]), c("0"=3, "1"=2, "2"=1, "3"=0))

All the columns are in order but instead of selecting by number like below

CTDB[,74:87] <-revalue(as.matrix(CTDB[,74:87]), c("0"=3, "1"=2, "2"=1, "3"=0))

I would like to select by the name of the column.

Thank you!

Do the columns you want to select all start with ENJOY_ and end with CHILD? And if so, do you want to select all of them? — Rui Barradas
– Rui Barradas, Commented Feb 9, 2018 at 18:50
@Onyambu I don't want the numbers, because the position of the columns can change in the dataset. — KKhosra
– KKhosra, Commented Feb 9, 2018 at 18:53
@RuiBarradas Yes, all the columns start with ENJOY_ and end with CHILD and yes I want to select everything that starts with ENJOY_ and ends with CHILD — KKhosra
– KKhosra, Commented Feb 9, 2018 at 18:55
what criterion can you use to identify the columns you need. What do they all have in common? — Onyambu
– Onyambu, Commented Feb 9, 2018 at 18:55

Onyambu · Accepted Answer · 2018-02-09 19:52:15Z

3

You should use grep or grepl

CTBD[,grep("^ENJOY.*CHILD$",colnames(CTBD)]

or

CTBD[,grepl("^ENJOY.*CHILD$",colnames(CTBD)]

edited Feb 9, 2018 at 19:52

answered Feb 9, 2018 at 18:57

Onyambu

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5 Comments

KKhosra Over a year ago

I got this error message: Error in grep("ENJOY.*CHILD", x) : object 'x' not found

KKhosra Over a year ago

Thank you! I got this warning message: "Warning message: In matrix(value, n, p) : data length [49890] is not a sub-multiple or multiple of the number of columns [14]" Do you know what it means?

Onyambu Over a year ago

are you trying to create another matrix? you have 14 columns but the datelength that you have cannot be divided into 14 columns

Rui Barradas Over a year ago

If CTBD is a matrix then you have to use colnames, which also works with data frames.

KKhosra Over a year ago

I still get this message "Warning message: In matrix(value, n, p) : data length [49890] is not a sub-multiple or multiple of the number of columns [14]"

Calum You · Accepted Answer · 2018-02-09 20:10:18Z

1

If you need to do this as part of a pipe, you can also use dplyr::select and its helper functions in two equivalent ways, including one that can avoid regular expressions:

CTBD %>% select(matches("^ENJOY.*CHILD$"))
CTBD %>% select(intersect(starts_with("ENJOY"), ends_with("CHILD")))

answered Feb 9, 2018 at 20:10

Calum You

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