which

问题 I'd like to grep for "nitrogen" in the following character vector and want to get back only the entry which is containing "nitrogen" and nothing of the rest (e.g. nitrogen fixation): varnames=c("nitrogen", "dissolved organic nitrogen", "nitrogen fixation", "total dissolved nitrogen", "total nitrogen") I tried something like this: grepl(pattern= "![[:space:]]nitrogen![[:space:]]", varnames) But this doesn't work. I hope somebody can help me with this task. 回答1: To get the indices that are

问题 This question already has answers here : Closed 8 years ago . Possible Duplicate: What sort algorithm provides the best worst-case performance? Which is the best method that can be used to sort an Integer array?Is Quick Sort efficient? Some of the common methods used for sorting are mentioned in [spam link removed] 回答1: They are different sorting methods are available with different features. Bubble Sort [It's simple but not good for large data][1] Selection Sort [Selection sort is noted for

问题 Based on a problem I discussed here: https://stackoverflow.com/a/57364028/2725773 I'm wondering what's the tolerance/precision of the which.max function in R. Specifically, the alternative max.col function has a tolerance of 1e-5, which means that 0.12345 is the same for it as 0.12346. The help page for max.col suggests an alternative, namely using unname(apply(m, 1, which.max)) , which brings me to the questions what's the tolerance of which.max ? 回答1: Fascinating question. I do not know the

问题 I am trying to determine which variables in my V1 column have values in the V5 column that are in the range of 95-105 and also have values in the V6 column that are in the 7-13 range. I am using the which function and attempting to store the names of the variables in V1 under the variable x but I keep getting the output integer(0) or character(0) and I'm not sure what that means. An image of my code is attached below. 回答1: integer(0) means there are no elements of your data frame that satisfy

问题 I am trying to find indexes within a data frame which holds a certain string. But I would like my string to be case insensitive. Say, I want to search for column number in my data frame called COLUMN73 and I expect it to return 73 because it is the seventy third column. I have, which(names(mydata) == "COLUMN73") Is it possible to make my search string case insensitive so as to get 73 even if I search for say, CoLumN73 ? Thanks. 回答1: You can convert your names to upper cases which(toupper

问题 This question already has answers here : Index values from a matrix using row, col indicies (4 answers) Closed last year . Given a matrix mat = matrix(round(runif(min=0,max=1,n=9*9)),ncol=9,nrow=9) say you want all the values of 1 using array indexing indx.1 = which(mat == 1, arr.ind=TRUE) How do you manipulate those index values within your matrix? The below doesn't accomplish what I am after: result.i.dont.want = mat result.i.dont.want[indx.1[,1],indx.1[,2]] = NA because, as far as I can

问题 This is a bash weirdness that's been bugging me. I'm on OSX. I've installed the android SDK, and as a result the adb tool is located in a folder in my home directory. That folder appears in my path as reported by env as ~/Development/android_sdk_latest/platform-tools . adb itself runs just fine, but when I do which adb the result is empty. If I do command -v adb , the result is the full path, as expected: /Users/me/Development/android_sdk_latest/platform-tools/adb adb does not appear in my

问题 I have a vector of positive and negative numbers vec<-c(seq(-100,-1), rep(0,20), seq(1,100)) the vector is larger than the example, and takes on a random set of values. I have to repetitively find the number of negative numbers in the vector... I am finding this is quite inefficient. Since I only need to find the number of negative numbers, and the vector is sorted, I only need to know the index of the first 0 or positive number (there may be no 0s in the actual random vectors). Currently I

问题 In R, let M be the matrix: [,1] [,2] [1,] 1 9 [2,] 3 12 [3,] 6 4 [4,] 7 2 I would like to extract all rows with entries equal to the components of the vector v <- c(3,6,1) from column [,1] in M producing the submatrix m: [,1] [,2] [1,] 1 9 [2,] 3 12 [3,] 6 4 I tried m <- M[which(M[,1] == v), ] obtaining the error message longer object length is not a multiple of shorter object length . Using the transpose t(v) of v does not help. Thanks a lot! Avitus 回答1: using %in% : M[M[,1] %in% v,] [,1] [

问题 I have a grouped data_frame with a "tag" column taking on values "0" and "1". In each group, I need to find the first occurrence of "1" and change all the remaining occurrences to "0". Is there a way to achieve it in dplyr? For example, let's take "iris" data and let's add the extra "tag" column: data(iris) set.seed(1) iris$tag <- sample( c(0, 1), 150, replace = TRUE, prob = c(0.8, 0.2)) giris <- iris %>% group_by(Species) In "giris", in the "setosa" group I need to keep only the first