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Test whether string is a valid integer
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[[ $var =~ ^-?[0-9]+$ ]]
The ^ indicates the beginning of the input pattern
The - is a literal "-"
The ? means "0 or 1 of the preceding (-)"
The + means "1 or more of the preceding ([0-9])"
The $ indicates the end of the input pattern
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In Python, how do you convert a `datetime` object to seconds?
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10 Answers
10
Active
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Ruby on Rails: How do you add add zeros in front of a number if it's under 10?
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Did you mean sprintf '%02d', n?
irb(main):003:0> sprintf '%02d', 1
=> "01"
irb(main):004:0> sprintf '%02d', 10
=> "10"
You might want to reference the format table for sprintf in the future, but for this particular example '%02d' mea...
How can I create a correlation matrix in R?
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104
An example,
d &lt- data.frame(x1=rnorm(10),
x2=rnorm(10),
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Which iOS app version/build number(s) MUST be incremented upon App Store release?
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10 Answers
10
Active
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Add new row to dataframe, at specific row-index, not appended?
...s the (often slow) rbind call:
existingDF <- as.data.frame(matrix(seq(20),nrow=5,ncol=4))
r <- 3
newrow <- seq(4)
insertRow <- function(existingDF, newrow, r) {
existingDF[seq(r+1,nrow(existingDF)+1),] <- existingDF[seq(r,nrow(existingDF)),]
existingDF[r,] <- newrow
existing...
How to read the content of a file to a string in C?
...-codes for fseek, ftell and fread. (omitted for clarity).
char * buffer = 0;
long length;
FILE * f = fopen (filename, "rb");
if (f)
{
fseek (f, 0, SEEK_END);
length = ftell (f);
fseek (f, 0, SEEK_SET);
buffer = malloc (length);
if (buffer)
{
fread (buffer, 1, length, f);
}
fclo...
Get the index of the nth occurrence of a string?
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10 Answers
10
Active
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Adding a y-axis label to secondary y-axis in matplotlib
...directly
import numpy as np
import matplotlib.pyplot as plt
x = np.arange(0, 10, 0.1)
y1 = 0.05 * x**2
y2 = -1 *y1
fig, ax1 = plt.subplots()
ax2 = ax1.twinx()
ax1.plot(x, y1, 'g-')
ax2.plot(x, y2, 'b-')
ax1.set_xlabel('X data')
ax1.set_ylabel('Y1 data', color='g')
ax2.set_ylabel('Y2 data', color...
How to sum a variable by group
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404
Using aggregate:
aggregate(x$Frequency, by=list(Category=x$Category), FUN=sum)
Category x
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