R index by column name

When subsetting with two indices, they behave like matrices, so df[1:3, ] selects One common mistake with $ is to use it when you have the name of a column  If TRUE , setting row names and converting column names (to syntactic names: see make.names ) is optional. Note that all of R's base package as.data.frame() 

An R tutorial on retrieving a collection of column vectors in a data frame with the single square operator. Discussion on usage of numeric and name indexing. To retrieve a data frame slice with the two columns mpg and hp, we pack the column names in an index vector inside the single square bracket operator. Rows to subset by. These may be numeric indices, character names, a logical mask, or a 2-d logical array col The columns to index by. If `row` is a 2-d array, this should not be given. value Provide a an empty vector of some type to specify the type of the output. R stores the row and column names in an attribute called dimnames. Use the dimnames() function to extract or set those values. Using names as indices. These row and column names can be used just like you use names for values in a vector. You can use these names instead of the index number to select values from a vector. Notice how only the “wt” column is renamed to “weight” and all of the other columns keep their original names. Renaming Columns by Index Using Base R. We can also rename a specific column in the mtcars dataset by index. For example, here is how to rename the second column name “cyl” by index: We recently saw a great recurring R question: “how do you use one column to choose a different value for each row?” That is: how do you use a column as an index? Please read on for some idiomatic base R, data.table, and dplyr solutions. Let’s say we have some example data: df

Column names. Description. Return all column names as a list. Usage. ## S4 method for signature 'DataFrame' columns(x) ## S4 method for signature 

To get the name of a column in an Excel Table from its numeric index, you can use the INDEX function with a structured reference. In the example shown, the  16 Jun 2018 Related: When all column names are integers or strings of integers, than pandas: only string indices, only string categories (like R's factors). We can pass a list of column names too, as an index to select columns in that This is different from other tools like R and Matlab that index elements within  Since the column names are an 'index' type, you can use .str on them too. You can fix all these lapses of judgement by chaining together a bunch of these .str  R's subsetting operators are powerful and fast. Character vectors to return elements with matching names. 1d subsetting: you supply a 1d index for each dimension, separated by a comma. Arrays in R are stored in column-major order:. 17 Oct 2017 Check the structure of data frame; Get column and row names of a data index mtcars[, 1] # mileage is the first columns # Using column name  2 Oct 2016 R - Rename column of data frame or Change column names of a the index of the column we want to change in the column names vector.

17 Oct 2017 Check the structure of data frame; Get column and row names of a data index mtcars[, 1] # mileage is the first columns # Using column name 

Unlike in some other programming languages, when you use negative numbers for indexing in R, it doesn’t mean to index backward from the end. Instead, it means to drop the element at that index, counting the usual way, from the beginning.

Get column index from label in a data frame. I need to get the column number of a column given its name. Supose we have the following dataframe: df <- data.frame(a=rnorm(100),b=rnorm(100),c=rnorm(100)) I need a function that would work like the following: getColumnNumber(df,"b") And it would return [1] 2 Is there a function like that? Thanks!

Notice how only the “wt” column is renamed to “weight” and all of the other columns keep their original names. Renaming Columns by Index Using Base R. We can also rename a specific column in the mtcars dataset by index. For example, here is how to rename the second column name “cyl” by index:

To get the name of a column in an Excel Table from its numeric index, you can use the INDEX function with a structured reference. In the example shown, the 

Renaming Columns of a Data Table in R. Contents: get column names colnames(my_data) It's also possible to rename by index in names vector as follow: Let's see how can we convert a column to row name/index in Pandas. Create a dataframe first with dict of lists. filter_none. edit close. play_arrow.

Cross Validated is a question and answer site for people interested in statistics, machine learning, data analysis, data mining, and data visualization. It only takes a minute to sign up. Finding the column index by its name in R [closed] In a data frame, I would like to get the column's index by name. R stores the row and column names in an attribute called dimnames. Use the dimnames() function to extract or set those values. Using names as indices. These row and column names can be used just like you use names for values in a vector. You can use these names instead of the index number to select values from a vector. As R user you will agree: To rename column names is one of the most often applied data manipulations in R. However, depending on your specific data situation, a different R syntax might be needed. However, depending on your specific data situation, a different R syntax might be needed. Unlike in some other programming languages, when you use negative numbers for indexing in R, it doesn’t mean to index backward from the end. Instead, it means to drop the element at that index, counting the usual way, from the beginning. Get column index from label in a data frame. I need to get the column number of a column given its name. Supose we have the following dataframe: df <- data.frame(a=rnorm(100),b=rnorm(100),c=rnorm(100)) I need a function that would work like the following: getColumnNumber(df,"b") And it would return [1] 2 Is there a function like that? Thanks! R : Delete column by name Method I : The most easiest way to drop columns is by using subset() All you just need to do is to mention the column index number. In the following code, we are telling R to drop variables that are positioned at first column, third and fourth columns. The minus sign is to drop variables. As mentioned by @snoram, you can give the new column any name you want, e.g. setDT(df, keep.rownames = "newname") would add "newname" as the rows column.