slice

问题 I'm getting a surprising result when selecting a 2D sub-slice of a slice. Consider the following 2D int array a := [][]int{ {0, 1, 2, 3}, {1, 2, 3, 4}, {2, 3, 4, 5}, {3, 4, 5, 6}, } To select the top left 3x3 2D slice using ranges I would use b := a[0:2][0:2] I would expect the result to be [[0 1 2] [1 2 3] [2 3 4]] however the second index range doesn't seem to have any effect, and returns the following instead: [[0 1 2 3] [1 2 3 4] [2 3 4 5]] What am I missing? Can you simply not select a

问题 In Golang, after asserting to a slice, how is one able to remove an element from said slice? For example, the following returns the error cannot assign to value.([]interface {}) value.([]interface{}) = append(value.([]interface{})[:i],value.([]interface{})[i+1:]...) 回答1: If you have a slice value wrapped in an interface, you can't change it. You can't change any value wrapped in interfaces. When an interface value is created to wrap a value, a copy is made and stored in the interface. When

问题 In Golang, after asserting to a slice, how is one able to remove an element from said slice? For example, the following returns the error cannot assign to value.([]interface {}) value.([]interface{}) = append(value.([]interface{})[:i],value.([]interface{})[i+1:]...) 回答1: If you have a slice value wrapped in an interface, you can't change it. You can't change any value wrapped in interfaces. When an interface value is created to wrap a value, a copy is made and stored in the interface. When

问题 I'm on Python 2.7. I have a dataframe with 200 columns and need to drop a few. I can use the below to drop the last n columns. How do I write it so i can drop the first 10, then column 22, then 26, 10th from the last, and last 5. All in one line. df2 = df.iloc[:, :-5] 回答1: Use np.r_: import numpy as np df.drop(df.columns[np.r_[:10, 22, 26, -10, -5:0]], axis=1) np.r_ concatenates several slices. For example, np.r_[1:3, 5, 7:9, -3:0] returns array([ 1, 2, 5, 7, 8, -3, -2, -1]) . You can use

问题 In Golang, we can use the builtin make() function to create a slice with a given initial length and capacity. Consider the following lines, the slice's length is set to 1, and its capacity 3: func main() { var slice = make([]int, 1, 3) slice[0] = 1 slice = append(slice, 6, 0, 2, 4, 3, 1) fmt.Println(slice) } I was surprised to see that this program prints: [1 6 0 2 4 3 1] This got me wondering- what is the point of initially defining a slice's capacity if append() can simply blow past it? Are

问题 In Golang, we can use the builtin make() function to create a slice with a given initial length and capacity. Consider the following lines, the slice's length is set to 1, and its capacity 3: func main() { var slice = make([]int, 1, 3) slice[0] = 1 slice = append(slice, 6, 0, 2, 4, 3, 1) fmt.Println(slice) } I was surprised to see that this program prints: [1 6 0 2 4 3 1] This got me wondering- what is the point of initially defining a slice's capacity if append() can simply blow past it? Are

问题 In Golang, we can use the builtin make() function to create a slice with a given initial length and capacity. Consider the following lines, the slice's length is set to 1, and its capacity 3: func main() { var slice = make([]int, 1, 3) slice[0] = 1 slice = append(slice, 6, 0, 2, 4, 3, 1) fmt.Println(slice) } I was surprised to see that this program prints: [1 6 0 2 4 3 1] This got me wondering- what is the point of initially defining a slice's capacity if append() can simply blow past it? Are

问题 In Golang, we can use the builtin make() function to create a slice with a given initial length and capacity. Consider the following lines, the slice's length is set to 1, and its capacity 3: func main() { var slice = make([]int, 1, 3) slice[0] = 1 slice = append(slice, 6, 0, 2, 4, 3, 1) fmt.Println(slice) } I was surprised to see that this program prints: [1 6 0 2 4 3 1] This got me wondering- what is the point of initially defining a slice's capacity if append() can simply blow past it? Are

问题 How to parse a string (which is an array) in Go using json package? type JsonType struct{ Array []string } func main(){ dataJson = `["1","2","3"]` arr := JsonType{} unmarshaled := json.Unmarshal([]byte(dataJson), &arr.Array) log.Printf("Unmarshaled: %v", unmarshaled) } 回答1: The return value of Unmarshal is an err, and this is what you are printing out: // Return value type of Unmarshal is error. err := json.Unmarshal([]byte(dataJson), &arr) You can get rid of the JsonType as well and just use

问题 I have data that is created rows by rows, 6 columns, I don't know the final number of rows in advance. Currently i'm creating a 2D slice of 200x6 with all zeros and then i replace these zeros gradually with my data, row by row. The data comes from another dataframe df It works but i don't like to end up with the last rows of my slice full of zeros. I see 2 solutions: - I delete all the last rows with only zeros when I'm done - I create an empty slice and append my data progressively to it I